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Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa20
Strategies of management for the whole treatment of leachates generated in a landfill and in a composting plant a
b
b
Juan García-López , Carlos Rad & Milagros Navarro a
Department of Civil Engineering, University of Burgos, EPS-La Milanera, Burgos, Spain
b
Composting Research Group (UBUCOMP), University of Burgos, EPS-La Milanera, Burgos, Spain Published online: 19 Aug 2014.
To cite this article: Juan García-López, Carlos Rad & Milagros Navarro (2014) Strategies of management for the whole treatment of leachates generated in a landfill and in a composting plant, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 49:13, 1520-1530, DOI: 10.1080/10934529.2014.938526 To link to this article: http://dx.doi.org/10.1080/10934529.2014.938526
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Journal of Environmental Science and Health, Part A (2014) 49, 1520–1530 Copyright © Taylor & Francis Group, LLC ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2014.938526
Strategies of management for the whole treatment of leachates generated in a landfill and in a composting plant 1 JUAN GARCIA-LOPEZ , CARLOS RAD2 and MILAGROS NAVARRO2 1
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Department of Civil Engineering, University of Burgos, EPS-La Milanera, Burgos, Spain Composting Research Group (UBUCOMP), University of Burgos, EPS-La Milanera, Burgos, Spain
This study compares the leachates generated in the treatment of Municipal Solid Wastes (MSW) of similar origin but managed in two different ways: (a) sorting and composting in a Treatment Plant in Aranda de Duero (Burgos, Spain), and (b) direct dumping in a landfill in Aranda de Duero (Burgos, Spain) with no prior treatment. Two different leachates were considered for the former: those generated in the fermentation shed (P1) and those generated in the composting tunnels (P2); another leachate was collected from the landfill (P3). Physical and chemical properties, including heavy metal contents, were seasonally monitored in the different leachates. This study allowed us to conclude that the sampling season had a significant effect on Pb, Cd, Ni, Mg and total-N contents (P < 0.01). Similarly, leachates P1, P2 and P3 exhibited significant overall differences for most of the measured parameters except for Cd, Cu, Pb, K, Fe, C-inorg and C-org contents (P < 0.01). This study concludes with the feasibility of a whole treatment for both leachates using ultrafiltration in a membrane bioreactor (MBR). Keywords: Leachate, landfill, composting plant, MBR, ultrafiltration, heavy metals.
Introduction The need to achieve an overall protection of the environment has increased over the past few years. The almost exponential population growth, changes in social and resource-use habits, higher output and consumption, our increasingly opulent lifestyles and the ongoing industrial and technological progress over the past 20 or 30 years, have been accompanied by an equally rapid increase in the generation of municipal and industrial solid waste worldwide.[1,2] The most common way of eliminating municipal solid wastes (MSW) is to dump them in a landfill site after treatment. Another alternative, although less widely used, is incineration. Landfill sites experience at least five waste decomposition stages, each of which results in the generation of different compounds and emissions.[3]: 1. Aerobic: The main products of this stage are water and carbon dioxide, the latter of which is either released as
Address correspondence to Juan García-L opez, Department of Civil Engineering, University of Burgos, EPS-La Milanera, Villadiego s/n, 09001 Burgos, Spain; E-mail: [email protected] Received March 2, 2014. Color versions of one or more figures in this article can be found online at www.tandfonline.com/lesa.
2. 3. 4. 5.
a gas or absorbed by the water to form carbonic acid, which acidifies the leachate. Acidogenic: Carbon dioxide, hydrogen, ammonia and organic acids. Acetogenic: Acetic acid and its derivatives, carbon dioxide and hydrogen. Methanogenic: The typical landfill gas composition: approximately 60% methane and 40% carbon dioxide. Aerobic: Carbon dioxide and water.
Leachate generated from landfills may have a long-term environmental impact for several centuries if proper management is overlooked.[4] Therefore, there is an urgent task to find an efficient technology to dispose of landfill leachates; otherwise, it will cause an important environmental risk since leachate leakage may contaminate ground and surface waters. Several biological and physicochemical techniques are used for treating MSW-leachate, such as modified sequencing batch reactors, anaerobic sludge blanket, coagulation, flotation, chemical precipitation, adsorption, etc. Biological methods can remove individual pollutants efficiently using mixed biological populations; and usually, the physicochemical techniques are adopted subsequently as refining processes. However, with the continuously stringent discharge standards in surface waters, the use of conventional biological methods combined with physicochemical treatments are no longer adequate to purify stabilized leachates from old landfill sites, which have a poor biodegradability.[5]
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Management of leachate treatment for landfill and composting plant Two main types of facilities are commonly used in Spain in the centralized treatment schemes of MSWs: a) manual or mechanical sorting and composting, and b) sorting, biomethanization and composting. Both types of facilities allow recovering recyclable materials, such as plastic, glass, or light packaging, and a biostabilized material (compost), which can be used as an organic soil conditioner after appropriate refining process. Composting is the biological decomposition of the organic components of waste, usually under aerobic conditions. This process reduces the volume of the waste and results in marked morphological and chemical changes in the organic material. [6] The main types of composting systems include turned or aerated windrows, closed-reactor and vessel-type systems.[7] During composting, organic matter is metabolically transformed into CO2 and H2O and the energy is used to synthesise microbiological biomass.[8] At the same time, a parallel process of humification is carried out by specific microorganisms with the most recalcitrant organic materials, which lead to the formation of a stabilised product with similar properties to soil humus, with beneficial effects for soil microbial activity and plant growth. Metabolic heat is also generated during the organic decomposition of biodegradable matter.[9] This process may destroy pathogens, parasites, worms and weed seeds, all of which represent a risk when this product is applied in the field.[10] Numerous studies regarding specific composting conditions have discussed specific aspects related to temperature, moisture content, aeration, pH and C/N ratio during the process.[11] Similarly, the use of a large variety of solid wastes in composting processes, including sewage sludge’s, crop wastes,[12,13] animal slurries,[10,14,15] and industrial biowastes,[16,17] has been investigated. A significant amount of leachate is produced in both, waste treatment facilities and landfill sites. The amount of leachate generated and the decomposition, stabilisation and extraction of contaminants from the waste matrix will depend on various factors, including the composition of the waste, its degree of compaction and its ability to absorb a wide variety of contaminants. Landfill leachate composition is often characterized by its high ammonia concentration, as compared with conventional single pass leaching.[18] Leachate recirculation during the first phase of waste decomposition leads to the accumulation of fermentation products, which primarily consist of volatile organic acids and alcohols because of the imbalance of the growth rates between fast-growing acidogenic bacteria and slow-growing methanogens. Consequently, methanogenesis may be delayed or inhibited.[19,20] Leachate produced in a landfill has a dark brown colour, normally has a very strong smell and contains high levels of contaminants (for example, a COD of 5,000 mg L¡1 in comparison with typical values of 100–200 mg L¡1 normally found in municipal wastewaters). This highly loaded leachate also contains a mixture of contaminants such as: (i) Inorganic species (ammonium, calcium,
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magnesium, sodium, potassium, iron, sulphates, chlorides and heavy metals such as cadmium, chromium, copper, lead, nickel and zinc), (ii) Organic compounds (dissolved organic matter, volatile fatty acids, humic and fulvic-like substances, and xenobiotic organic compounds generally present in concentrations of less than 1 mg L¡1), and (iii) pathogenic microorganisms.[3,21,22] Although the source of and the problems derived from leachates are well known, there is little information regarding the differences between leachates generated in a MSWlandfill site and those produced in a MSW-Treatment Plant. The importance of the leachate generated by centralized facilities is sometimes neglected, giving priority to the whole treatment of MSW, the appropriate deposit of rejected materials and the amount of recycled components. Furthermore, the leachate generated in a landfill is usually treated directly in a wastewater treatment plant, which causes consequent problems in the performance of the biological reactor and the accumulation of their metal content into the sludge. The aim of this study was to compare the composition of a leachate generated in a MSW-Treatment Plant (aerobic process) with that produced in an adjacent sealed MSWlandfill site (anaerobic process) and to study the feasibility to treat both leachates using a biological process in a Membrane Biological Reactor (MBR). Furthermore, the effect of seasonal variations (spring, summer, autumn and winter) on the physicochemical properties of the leachates was also studied.
Materials and methods Description of the MSW-treatment plant in Aranda de Duero (Burgos, Spain) The Municipal Solid Waste Treatment Plant (MSW-TP) processes urban wastes produced in a total of 161 small villages around the main town of Aranda de Duero (Burgos, Spain), 41 41’ 53’’ N 03 43’ 02’’ W, approximately 29,000 tonnes year¡1. After a partial segregation at source, mixed MSWs were collected and transported using withdrawal trucks form different transfer places to the MSWTP, according with a centralized scheme of MSW-management (Fig. 1). MSW enters the facility in MSW-collection trucks, and thereafter it is manually sorted and the organic fraction separated on a conveyor belt by the use of a rotary trommel of 5 mm mesh. This fraction is subsequently introduced into composting tunnels, where it performs a 15 days active decomposition step under controlled conditions of humidity, temperature and aeration. After this time it is sent to a covered fermentation shed for another four weeks of aerobic fermentation in windrows, where it is weakly turned and moisturized. The resulting biostabilized material is sieved and refined ( P2 > P1) indicates that the concentration of Cr is higher in P3 than in P2 and, in turn, higher in P2 than in P1. These results are displayed in Figure 2.
Table 1. Physical and chemical parameters. Parameters pH EC (dS m¡1) DM (%) a 60 C Density (g m¡1) COD (mg L¡1) BOD (mg L¡1) COD/BOD TS (mg L¡1) SS (mg L¡1) VS (mg L¡1) C total (mg L¡1) C inorg (mg L¡1) TOC (mg L¡1) N total (mg L¡1) N org (mg L¡1) N-NH4C(mg L¡1) N-NO3¡ C NO2¡ (mg L¡1) PO43¡ (mg L¡1)
P1.1
P2.1
P3.1
P1.2
P2.2
P3.2
7.7 § 0.2 11.7 § 0.2 0.702 § 0.090 0.998 § 0.020 4097 § 1439 200 § 4 20 7005 § 886 1123 § 173 1562 § 245 2354 § 1 1620 § 0 735 § 0 851 § 0 181 § 2 670 § 19 n.d. 26 § 1
7.6 § 0.2 8.6 § 0.2 0.425 § 0.014 0.998 § 0.020 11585 § 998 1260 § 25 9 4236 § 132 2059 § 204 1998 § 218 5400 § 1 1136 § 0 4265 § 0 1445 § 1 680 § 27 765 § 35 n.d. 83 § 2
8.1 § 0.2 54.9 § 1.1 4.593 § 0.616 1.023 § 0.020 16812 § 0 600 § 12 28 46842 § 6581 597 § 36 27854 § 15 11950 § 4 684 § 0 11266 § 0 6805 § 3 783 § 133 6022 § 52 n.d. 83 § 2
7.7 § 0.2 23.8 § 0.5 1.542 § 0.150 0.998 § 0.020 12042 § 1485 300 § 6 40 15496 § 1539 1349 § 154 5150 § 1262 3477 § 2 2200 § 1 1277 § 2 1494 § 1 218 § 47 1276 § 80 n.d. 18 § 0
6.9 § 0.1 36.0 § 0.7 3.098 § 0.079 1.001 § 0.020 40758 § 2008 700 § 14 58 31249 § 739 10171 § 1788 14124 § 241 7685 § 1 1008 § 15 6677 § 16 2853 § 0 591 § 2 2262 § 14 n.d. 82 § 2
8.0 § 0.2 61.2 § 1.2 5.353 § 0.251 1.026 § 0.021 24589 § 1747 440 § 9 56 54775 § 2662 1020 § 52 31695 § 1885 12820 § 2 694 § 0 12127 § 0 7165 § 1 416 § 172 6749 § 160 n.d. 85 § 12
Analytical results for leachates P1, P2 and P3 for samples collected in spring and summer (n.d. under de limit of detection).
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Table 2. Physical and chemical parameters.
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Parameters pH EC (dS m¡1) DM (%) a 60 C Density (g m¡1) COD (mg L¡1) BOD (mg L¡1) COD/BOD TS (mg L¡1) SS (mg L¡1) VS (mg L¡1) C total (mg L¡1) C inorg (mg L¡1) TOC (mg L¡1) N total (mg L¡1) N org (mg L¡1) N-NH4C(mg L¡1) N-NO3¡ C NO2¡ (mg L¡1) PO43¡ (mg L¡1)
P1.3
P2.3
P3.3
P1.4
P2.4
P3.4
7.4 § 0.1 19.9 § 0.4 1.150 § 0.019 0.999 § 0.020 26154 § 523 4230 § 85 6 11524 § 182 1203 § 233 2144 § 48 4591 § 0 1685 § 1 2906 § 0 1181 § 0 444 § 12 737 § 45 n.d. 22 § 1
7.6 § 0.2 24.1 § 0.5 1.805 § 0.012 1.001 § 0.020 25066 § 501 7740 § 155 3 18182 § 150 4234 § 304 6034 § 99 6695 § 2 431 § 1 6264 § 1 1612 § 1 630 § 29 982 § 33 n.d. 87 § 0
7.7 § 0.2 59.7 § 1.2 5.125 § 0.358 1.013 § 0.020 16982 § 340 880 § 18 19 52525 § 3607 577 § 52 29048 § 3181 12320 § 1 706 § 1 11614 § 1 6680 § 0 410 § 132 6270 § 269 n.d. 84 § 2
7.4 § 0.1 20.4 § 0.4 1.586 § 0.023 0.999 § 0.020 21420 § 428 3715 § 74 6 15908 § 252 1755 § 542 6559 § 63 4145 § 232 1625 § 1 2520 § 263 1933 § 14 799 § 907 1134 § 63 0§0 3§0
7.4 § 0.1 18.2 § 0.4 1.807 § 0.208 1.001 § 0.020 37560 § 751 5813 § 116 6 18034 § 2057 11862 § 11515 10059 § 879 7891 § 33 1631 § 1 6260 § 26 3213 § 1 1625 § 53 1588 § 36 3§0 12 § 1
8.0 § 0.2 65.8 § 1.3 2.864 § 0.238 1.025 § 0.021 9538 § 191 715 § 14 13 29339 § 2452 933 § 13 5265 § 2210 11550 § 1 4871 § 1 6679 § 0 9255 § 0 8008 § 44 1247 § 90 9§1 124 § 1
Analytical results for leachates P1, P2 and P3 for samples collected in autumn and winter (n.d. under de limit of detection).
Heavy metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn) The results obtained are as follows: Spring: Cd (P3 > P2 P1), Cr (P3 > P2 > P1), Cu (P3 > P1 > P2), Mn (P2 > P1 > P3), Ni (P3 > P1 P2), Pb (P2 > P3 > P1), Zn (P2 > P1 P3). Summer: Cd (P2 > P3 P1), Cr (P3 > P2 > P1), Cu (P3 > P1 > P2), Mn (P2 > P1 > P3), Ni (P2 > P3 > P1), Pb (P2 > P1 > P3), Zn (P2 > P1 P3). Autumn: Cd (P2 > P1 P3), Cr (P3 > P2 > P1), Cu (P3 > P2 > P1), Mn (P2 > P1 > P3), Ni (P3 > P2 > P1), Pb (P1 > P2 > P3), Zn (P2 > P1 > P3). Winter: Cd (P3 > > P2 > P1), Cr (P3 > P2 > P1), Cu (P3 > P2 > P1), Mn (P2 > P1 > P3), Ni (P2 > P3 > P1), Pb (P3 > P2 > P1), Zn (P2 > P1 > P3). Mean: Cd (P3 > P2 > P1), Cr (P3 > P2 > P1), Cu (P3 > P2 > P1), Mn (P2 > P1 > P3), Ni (P3 > P2 > P1), Pb (P2 > P3 > P1), Zn (P2 > P1 > P3).
The origin and composition of MSWs that produce both leachates are similar, which lead us to hypothesize a
similar concentration of heavy metals in the leachates produced in the MSW-Treatment Plant (MSW-TP) and the MSW-landfill site. Furthermore, as discussed above, the implementation of separate collection, the absence of IW in MSW, etc., the composition of MSW derived to the landfill site is likely to have a higher metal concentration than those of the MSW delivered to the MSW-TP. The main difference between both would be the way in which the waste that generates the leachate is “stored” and the different chemical and biological processes that occur in the MSW-landfill site and in the MSW-TP. Thus, the waste in the MSW-TP is produced in an oxidising environment (active composting phase: fermentation in tunnels; passive phase: fermentation shed), whereas the waste in the landfill site is produced in a reducing environment (lack of oxygen in the mass of residue stored in the landfill: anaerobiosis). However, in contrast to our initial expectations, the concentration of Mn, Pb and Zn in leachates P1 and P2 was higher than in leachate P3. Although, the concentration of the remaining heavy metals (Cd, Cr, Cu and Ni) was higher in P3 than in P2, and higher in P2 than in P1.
Table 3. TS, VS and VS/TS values for leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean values obtained. Spring P1 TS VS VS/TS
P2
Summer P3
7005 4236 46842 1562 1998 27854 22% 47% 59% P3 > P2 > P1
P1
P2
Autumn P3
15496 31249 54775 5150 14124 31695 33% 45% 58% P3 > P2 > P1
P1
P2
Winter P3
11524 18182 52525 2114 6034 29048 18% 33% 55% P3 > P2 > P1
P1
P2
Mean P3
15908 18034 29339 6559 10059 5265 41% 56% 18% P2 > P1 > P3
P1
P2
P3
12483 17925 45870 3846 8054 23466 31% 45% 51% P3 > P2 > P1
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Fig. 2. Heavy metal contents of Cd, Cr, Cu, Mn, Ni and Pb, in leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean values.
Fig. 3. Heavy metal contents of Zn, and other metallic elements Na, K, Ca, Mg and Fe in leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean values.
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The most likely explanation for the higher concentration of Mn, Pb and Zn found in leachates P1 and P2 would be the different chemical reactions that occur in these wastes in the two environments under study, where pH plays a key role. Thus, inside the landfill site, heavy metals are linked to the organic matter (OM) present in the waste, which makes their subsequent separation and leaching much slow and/or difficult. In contrast, in the composting process, leaching of Mn, Pb and Zn is greater despite their apparently lower initial concentration. Thus would explain why leachate P2 presents a 2731%, 425% and 22% higher concentration of Mn, Zn and Pb, respectively, than leachate P3, and why leachate P1 exhibits a 579% and 28% higher concentration of Mn and Zn, respectively, than leachate P3. Other elements (Na, K, Ca, Mg, Fe) can be found in Figure 3. The results obtained are as follows: Spring: Na (P3 > P1 > P2), K (P3 > P1 > P2), Ca (P2 > P1 > P3), Mg (P1 > P2 > P3) and Fe (P3 > P2 > P1). Summer: Na (P3 > P2 > P1), K (P2 > P1 > P3), Ca (P2 > P1 > P3), Mg (P2 > P1 > P3) and Fe (P2 > P3 > P1). Autumn: Na (P3 > P2 > P1), K (P2 > P3 > P1), Ca (P2 > P1 > P3), Mg (P2 > P1 > P3) and Fe (P3 P2 > P1). Winter: Na (P3 > P1 > P2), K (P3 > P1 > P2), Ca (P2 > P1 > P3), Mg (P1 > P2 > P3) and Fe (P2 > P1 > P3). Mean: Na (P3 > P1 P2), K (P3 > P2 P1), Ca (P2 > P1 > P3), Mg (P1 > P2 > P3) and Fe (P2 > P3 > P1).
García-L opez et al. The values for Na and K agree well with the EC values. The main difference between the EC for leachate P3 (60.41 dS m¡1) and those for leachates P1 and P2 (18.95 and 21.73 dS m¡1, respectively) arises due to the different mean Na and K concentration in P3 with respect to P1 (241% and 34% higher for the former, respectively) and P2 (245% and 33% higher for the former, respectively). It may be the case that Na and K form more stable bonds to OM particles in the composting tunnels and fermentation sheds than in the sealed landfill site. The opposite is found for Ca and Mg, both of which are present in higher concentrations in leachates P1 (612% and 565%, respectively) and P2 (2226% and 511%, respectively) than in leachate P3. This can be explained on the basis of the different mean pH values for leachate P3 (7.9) and leachates P1 and P2 (7.6 and 7.4, respectively). Ca and Mg are strongly leached from the landfill site due to anaerobic decomposition of the waste mass. In contrast, in the composting tunnels and fermentation shed, Ca and Mg are more strongly bound to, and stabilised by, OM particles and some proteins and are therefore leached to a lesser extent. Finally, the Fe concentration in all three leachates varies markedly with season and not displayed a clear pattern of variation with the origin of the leachate. Evolution of the chemical properties of the leachates Other parameters (TOC, SS, VS, N-total, N-NH4C, N-organic) can be found in Figure 4. The results obtained are as follows:
Fig. 4. TOC, N-total, N-NH4C, SS, VS and TS in leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean.
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Spring: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P3 > P2 > P1). Summer: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P2 > P3 > P1). Autumn: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P2 > P1 > P3). Winter: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P2 > P3 > P1), N-total (P3 > P2 > P1), N-NH4C (P2 > P3 > P1) and N-organic (P3 > P2 > P1). Mean: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P3 > P2 > P1).
The fact that mean values of COT, N-Total, N-NH4C and N-org for leachate P3 are much higher than those for leachates P1 and P2 is easily explained. Thus, P3 exhibits 78% higher TOC, 228% higher N-total, 173% higher NNH4C and 262% higher N-org values than P2. Furthermore, the TS value is higher for P3 than for P2, and for P2 than for P1. As can be seen from Table 3, a similar situation is found for VS (except for the winter sample), thus agreeing with the potential biogas production capacity of anaerobic digestion. The higher TOC content for P3 is due to the washout of recalcitrant OM, which requires more time to be decomposed by anaerobic than for aerobic processes. The majority of these volatile solids are converted into CH4, CO2, NH3, etc. with time, whereas in bio-oxidative processes part of the carbon remains un-volatilized and is converted into humus. A similar situation is found for nitrification. Thus, as most nitrogen is present in the ammonium form, a longer period of time is required for some of this nitrogen to be converted into nitrate. Furthermore, a significant amount of the N present would be lost by volatilization during the process.
The reason why the SS value is lower for leachate P3 than for leachates P1 and P2 is probably related to the sample collection method. Thus, sample P3 is collected using a small ladle whereas, due to their restricted access, samples P1 and P2 are obtained using a submersible pump. The TS and VS/TS ratio values can be found in Table 3. The results obtained were analysed using an ANOVA with two fixed factors, namely leachate type (three levels, P1, P2 and P3) and season of year when the sample was obtained (four levels, four seasons). Although the differences obtained for Cd, Cu, Pb, K, Fe, C-inorg, C-org were not significant for any leachate type, statistically significant differences with leachate type were obtained for Cr, Mn, Ni, Zn, Na, Ca, Mg, TS, SS, VS, C-total, TOC, Ntotal, N-NH4C and PO43¡ (P < 0.01). The season when the samples were collected was only significant for Pb, Cd, Ni, Mg and N-total (P < 0.01). The overall bivariate Pearson’s correlations coefficients between heavy metals and the other elements in leachates P1, P2 and P3 can be found in Table 4. The degree of bivariate correlation using the Pearson coefficient indicates the degree of correlation between two variables. The main finding of this part of the study was that the presence of metals such as Cd, Cr, Zn and Mn in the leachate was strongly correlated with the of other metals such as Pb, Na, Mn, Ca and Fe, which suppose similar leaching mechanisms besides the different processes affecting the evolution of MSWs in the MSW-TC and in the landfill. Thus, the Cd content in the leachates was highly correlated with the content of Pb (89%) with a significance of 99%. Similarly, Cr was correlated with Na (89%), Zn with Mn, Ca and Fe (83%, 78% and 74%, respectively) and, finally the Mn content of the leachates was correlated to Ca and Fe (74% and 70%, respectively). Use of MBR in leachates depuration Zhao et al.[24] reported that aged refuse reactors have long been used for the cost-effective treatment of landfill
Table 4. Bivariate correlations between heavy metals and other metallic elements in leachates P1, P2 and P3.
[Cu] [Ni] [Cd] [Pb] [Cr] [Zn] [Mn] [Fe] [Ca] [Mg] [K] [Na]
[Cu]
[Ni]
[Cd]
[Pb]
1 0.247 ¡0.138 ¡0.157 0.331* ¡0.195 ¡0.328 ¡0.128 ¡0.268 ¡0.198 0.324 0.464**
1 0.675** 0.596** 0.641** 0.424** 0.113 0.381* 0.302 0.229 0.652** 0.738**
1 0.943** 0.311 0.224 0.075 0.047 0.295 0.723** 0.332* 0.337*
1 0.170 0.251 0.136 0.029 0.379* 0.761** 0.292 0.209
*95% probability. **99% probability.
[Cr]
[Zn]
[Mn]
[Fe]
[Ca]
[Mg]
[K]
1 ¡0.253 1 ¡0.445** 0.910** 1 ¡0.030 0.858** 0.836** 1 ¡0.445** 0.884** 0.861** 0.682** 1 ¡0.377* 0.319 0.279 ¡0.003 0.531** 1 0.400* 0.037 ¡0.268 ¡0.077 0.042 0.149 1 0.946** ¡0.218 ¡0.496** ¡0.067 ¡0.369* ¡0.266 0.613**
[Na]
1
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Table 5. Global performance of the MBR using different mixtures of leachates. Parameters
Heavy metals
Elements
Leachate mixtures
TOC
N total
N-NH4C
Cd
Cu
Ni
Pb
Zn
Cr
Mn
Fe
Na
K
Ca
Mg
LE100P2-LP100P2 LE75P2P3-LP75P2P3 LE50P2P3-LP50P2P3 LE100P1-LP100P1 LE50P1P3-LP50P1P3
80% 91% 79% 98% 100%
51% 57% 11% 38% 82%
30% 35% 13% 8% 83%
58% 52% 42% 23% 45%
58% 40% 21% 28% 47%
98% 92% 26% 42% 86%
46% 71% 21% 13% 59%
97% 96% 88% 77% 88%
81% 94% 70% 69% 98%
98% 96% 88% 77% 68%
93% 95% 83% 96% 99%
18% 27% 20% 0% 78%
29% 16% 19% 23% 58%
91% 94% 84% 78% 73%
21% 42% 36% 23% 13%
Ca
Mg
92% 87% 73% 88% 93%
37% 28% 33% 34% 37%
Table 6. Performance of the ultrafiltrationdevice operating with the MBR effluent at different ratios of leachates. Parameters
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Leachate mixtures
TOC
LE100P2-LP100P2 81% LE75P2P3-LP75P2P3 83% LE50P2P3-LP50P2P3 71% LE100P1-LP100P1 97% LE50P1P3-LP50P1P3 100%
Heavy metals
N total N-NH4C 49% 33% 22% 40% 39%
19% 4% 3% 21% 28%
Elements
Cd
Cu
Ni
Pb
Zn
Cr
57% 36% 45% 37% 85%
66% 15% 95% 75% 51%
99% 86% 19% 72% 76%
42% 57% 39% 23% 55%
97% 92% 87% 90% 93%
86% 87% 82% 89% 78%
leachate. Moreover, the chemical oxygen demand (COD), biological oxygen demand, and ammonia–nitrogen (NH3– N) content can be reduced, thereby making the effluent clear and odorless.[25] Xie et al.[26] constructed aged refuse bioreactors to simulate the landfill leachate degradation process. Their results show that the aged refuse bioreactor could effectively remove leachate pollutants at a hydraulic loading rate of 20 m3 d¡1. However, the aged refuse bioreactor can often be blocked during operation, which could deteriorate the effluent quality. Recently, MBR technology, an advanced biological treatment process that replaces the traditional secondary clarifier of an activated sludge process by a membrane separation unit, has emerged as a promising alternative. The MBR technology has been applied to the treatment of contaminants in both municipal and industrial wastewater.[27,28] MBR technology provides biological treatment with membrane separation.[29,30] The system consists of an aerated water-filled tank containing activated sludge and multiple capillary-form membrane tubes. The pores of ultrafiltration membranes are approximately 20–50 nm in diameter, which effectively retains microorganisms, macromolecules and suspended solids. Microorganisms use the contaminants as nutrients for growth and metabolism. Results from the reatment of the leachates can be found in Tables 5 and 6 for the different leachates and their mixtures. The global performance of the biological process, with and without decantation, and the performance in the membranes were analyzed. The global performance was very high with an important decrease in the TOC contents in all of the cases. In general, this decrease in the contents
Mn
Fe
Na
K
97% 93% 3% 13% 92% 98% 5% 19% 86% 97% 15% 31% 94% 99% 4% 9% 95% 100% 4% 11%
of N-total and N-NH4C in leachate was not as good as the organic content elimination, but level of depuration was important in same cases (82% and 83%, respectively). The reduction in the heavy metal content of leachates was also important. Maximum reductions were reached in Ni, Cr and Mn contents (98%), Zn (97%), Pb (71%), and Cd and Cu (58%). The better performance was obtained with the content of Fe and Ca which reached 99% and 94% of the initial concentration, respectively. In general, the decrease was lower for alkaline metals such as Na, K and Mg contents. The membrane yield in the ultrafiltration process was very high with the TOC, reaching the maximum 100%, and with the concentration of heavy metals Ni, Mn, Zn, Cu, Cr, Cd and Pb in which reductions of 99%, 97%, 97%, 95%, 89%, 85%, 57% were reached for these metals, respectively. With the elements Fe, Ca, Mg, K and Na the maximum amounts in metal reduction were 100%, 93%, 37%, 31% and 15%, respectively.
Conclusions The leachate from the landfill site exhibited a higher TS content than those from the MSW-TP. Furthermore, the percentage of VS with respect to TS was also higher for the landfill site. A similar situation was found for TOC, N-total and N-NH4C. No significant differences in the contents of Cd, Cu, Pb, K, Fe, C-inorg or C-org were found between leachates of different origin. The sampling time significantly affected the concentration of Pb, Cd, Ni, Mg and N-total in leachates (P < 0.01).
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Management of leachate treatment for landfill and composting plant The Mn, Zn and, to a lesser extent, Pb present in MSWs were found to leach more readily in an oxidising (composting process) than in a reducing environment (anaerobic digestion). The presence of certain metals, such as Cd, Cr, Zn and Mn, in the leachate has been found to be strongly correlated with the presence of other metals such as Pb, Na, Mn, Ca and Fe. Usually, a combinations of physical, chemical and biological methods for landfill leachate treatment, is more efficient than using one of these methods separately. In general, the use of a MBR with ultrafiltration is a good tool to treat in a similar way, leachates from MSWTP and landfill. Removal efficiency values from 20% to over of 90% in chemical oxygen demand (COD) were achieved according to leachate characteristics (origin and age), process type and process operational aspects. Nitrification is generally readily achievable, with >95% removal of ammonia reported through the exclusive application of biological techniques to the treatment of both young and old leachates.
[9]
[10]
[11]
[12]
[13]
[14]
[15]
Funding [16]
This work was partially financed by VALORIZA, the commercial firm managing the MSW treatment centre of Aranda de Duero (Burgos, Spain). [17]
References [1] Ojeda-Benítez, S.; Beraud-Lozano, J.L. The municipal solid waste cycle in Mexico: final disposal. Resour. Conserv. Recycl. 2003, 39, 239–250. [2] Renou, S.; Givaudan, J.G.; Poulain, S.; Dirassouyan, F.; Moulin, P. Landfill leachate treatment: review and opportunity. J. Hazard. Mater. 2008, 150, 468–493. [3] Englehardt, J.D.; Deng, Y.; Polar, J.; Meeroff, D.E.; Legrenzi, Y.; Mognol, J. Options for Managing Municipal Landfill Leachate: Year 1. Development of Iron-mediated Treatment Processes, 2006, Report #0432024-06, State University System of Florida, Florida Center for Solid and Hazardous Waste Management, Gainesville, FL, USA. [4] Cossu, R.; Raga, R.; Rossetti, D. The PAF model: an integrated approach for landfill sustainability. Waste Manage. 2003, 23, 37–44. [5] Zou, D., Chi, Y., Dong, J., Fu, C., Ni, M. Supercritical Water Oxidation of MSW Leachate: Factor Analysis and Behavior of Heavy Metals. Environ. Prog. Sustainable Energy 2013, DOI 10.1002/ep. [6] Alburquerque, J.A.; Bautista-Carrascosa, I.; Lid on, A.; García-dela-Fuente, R.; Girbent, J.; Abad, M.; Cegarra, J. Co-composting an animal fatty-proteinaceous waste with a solid lignocellulosic by-product from the olive oil industry (‘alperujo’). J. Chem. Technol. Biotechnol. 2009, 84, 918–926. [7] Peigne, J.; Girardin, P. Environmental impacts of farm-scale composting practices. Water Air Soil Pollut. 2004, 153, 45–68. [8] Hartlieb, N.; Ertunc, T.; Schaeffer, A.; Klein, W. Mineralization, metabolism and formation of non-extractable residues of 14C-labelled organic contaminants during pilot-scale
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Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa20
Strategies of management for the whole treatment of leachates generated in a landfill and in a composting plant a
b
b
Juan García-López , Carlos Rad & Milagros Navarro a
Department of Civil Engineering, University of Burgos, EPS-La Milanera, Burgos, Spain
b
Composting Research Group (UBUCOMP), University of Burgos, EPS-La Milanera, Burgos, Spain Published online: 19 Aug 2014.
To cite this article: Juan García-López, Carlos Rad & Milagros Navarro (2014) Strategies of management for the whole treatment of leachates generated in a landfill and in a composting plant, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and Environmental Engineering, 49:13, 1520-1530, DOI: 10.1080/10934529.2014.938526 To link to this article: http://dx.doi.org/10.1080/10934529.2014.938526
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Journal of Environmental Science and Health, Part A (2014) 49, 1520–1530 Copyright © Taylor & Francis Group, LLC ISSN: 1093-4529 (Print); 1532-4117 (Online) DOI: 10.1080/10934529.2014.938526
Strategies of management for the whole treatment of leachates generated in a landfill and in a composting plant 1 JUAN GARCIA-LOPEZ , CARLOS RAD2 and MILAGROS NAVARRO2 1
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2
Department of Civil Engineering, University of Burgos, EPS-La Milanera, Burgos, Spain Composting Research Group (UBUCOMP), University of Burgos, EPS-La Milanera, Burgos, Spain
This study compares the leachates generated in the treatment of Municipal Solid Wastes (MSW) of similar origin but managed in two different ways: (a) sorting and composting in a Treatment Plant in Aranda de Duero (Burgos, Spain), and (b) direct dumping in a landfill in Aranda de Duero (Burgos, Spain) with no prior treatment. Two different leachates were considered for the former: those generated in the fermentation shed (P1) and those generated in the composting tunnels (P2); another leachate was collected from the landfill (P3). Physical and chemical properties, including heavy metal contents, were seasonally monitored in the different leachates. This study allowed us to conclude that the sampling season had a significant effect on Pb, Cd, Ni, Mg and total-N contents (P < 0.01). Similarly, leachates P1, P2 and P3 exhibited significant overall differences for most of the measured parameters except for Cd, Cu, Pb, K, Fe, C-inorg and C-org contents (P < 0.01). This study concludes with the feasibility of a whole treatment for both leachates using ultrafiltration in a membrane bioreactor (MBR). Keywords: Leachate, landfill, composting plant, MBR, ultrafiltration, heavy metals.
Introduction The need to achieve an overall protection of the environment has increased over the past few years. The almost exponential population growth, changes in social and resource-use habits, higher output and consumption, our increasingly opulent lifestyles and the ongoing industrial and technological progress over the past 20 or 30 years, have been accompanied by an equally rapid increase in the generation of municipal and industrial solid waste worldwide.[1,2] The most common way of eliminating municipal solid wastes (MSW) is to dump them in a landfill site after treatment. Another alternative, although less widely used, is incineration. Landfill sites experience at least five waste decomposition stages, each of which results in the generation of different compounds and emissions.[3]: 1. Aerobic: The main products of this stage are water and carbon dioxide, the latter of which is either released as
Address correspondence to Juan García-L opez, Department of Civil Engineering, University of Burgos, EPS-La Milanera, Villadiego s/n, 09001 Burgos, Spain; E-mail: [email protected] Received March 2, 2014. Color versions of one or more figures in this article can be found online at www.tandfonline.com/lesa.
2. 3. 4. 5.
a gas or absorbed by the water to form carbonic acid, which acidifies the leachate. Acidogenic: Carbon dioxide, hydrogen, ammonia and organic acids. Acetogenic: Acetic acid and its derivatives, carbon dioxide and hydrogen. Methanogenic: The typical landfill gas composition: approximately 60% methane and 40% carbon dioxide. Aerobic: Carbon dioxide and water.
Leachate generated from landfills may have a long-term environmental impact for several centuries if proper management is overlooked.[4] Therefore, there is an urgent task to find an efficient technology to dispose of landfill leachates; otherwise, it will cause an important environmental risk since leachate leakage may contaminate ground and surface waters. Several biological and physicochemical techniques are used for treating MSW-leachate, such as modified sequencing batch reactors, anaerobic sludge blanket, coagulation, flotation, chemical precipitation, adsorption, etc. Biological methods can remove individual pollutants efficiently using mixed biological populations; and usually, the physicochemical techniques are adopted subsequently as refining processes. However, with the continuously stringent discharge standards in surface waters, the use of conventional biological methods combined with physicochemical treatments are no longer adequate to purify stabilized leachates from old landfill sites, which have a poor biodegradability.[5]
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Management of leachate treatment for landfill and composting plant Two main types of facilities are commonly used in Spain in the centralized treatment schemes of MSWs: a) manual or mechanical sorting and composting, and b) sorting, biomethanization and composting. Both types of facilities allow recovering recyclable materials, such as plastic, glass, or light packaging, and a biostabilized material (compost), which can be used as an organic soil conditioner after appropriate refining process. Composting is the biological decomposition of the organic components of waste, usually under aerobic conditions. This process reduces the volume of the waste and results in marked morphological and chemical changes in the organic material. [6] The main types of composting systems include turned or aerated windrows, closed-reactor and vessel-type systems.[7] During composting, organic matter is metabolically transformed into CO2 and H2O and the energy is used to synthesise microbiological biomass.[8] At the same time, a parallel process of humification is carried out by specific microorganisms with the most recalcitrant organic materials, which lead to the formation of a stabilised product with similar properties to soil humus, with beneficial effects for soil microbial activity and plant growth. Metabolic heat is also generated during the organic decomposition of biodegradable matter.[9] This process may destroy pathogens, parasites, worms and weed seeds, all of which represent a risk when this product is applied in the field.[10] Numerous studies regarding specific composting conditions have discussed specific aspects related to temperature, moisture content, aeration, pH and C/N ratio during the process.[11] Similarly, the use of a large variety of solid wastes in composting processes, including sewage sludge’s, crop wastes,[12,13] animal slurries,[10,14,15] and industrial biowastes,[16,17] has been investigated. A significant amount of leachate is produced in both, waste treatment facilities and landfill sites. The amount of leachate generated and the decomposition, stabilisation and extraction of contaminants from the waste matrix will depend on various factors, including the composition of the waste, its degree of compaction and its ability to absorb a wide variety of contaminants. Landfill leachate composition is often characterized by its high ammonia concentration, as compared with conventional single pass leaching.[18] Leachate recirculation during the first phase of waste decomposition leads to the accumulation of fermentation products, which primarily consist of volatile organic acids and alcohols because of the imbalance of the growth rates between fast-growing acidogenic bacteria and slow-growing methanogens. Consequently, methanogenesis may be delayed or inhibited.[19,20] Leachate produced in a landfill has a dark brown colour, normally has a very strong smell and contains high levels of contaminants (for example, a COD of 5,000 mg L¡1 in comparison with typical values of 100–200 mg L¡1 normally found in municipal wastewaters). This highly loaded leachate also contains a mixture of contaminants such as: (i) Inorganic species (ammonium, calcium,
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magnesium, sodium, potassium, iron, sulphates, chlorides and heavy metals such as cadmium, chromium, copper, lead, nickel and zinc), (ii) Organic compounds (dissolved organic matter, volatile fatty acids, humic and fulvic-like substances, and xenobiotic organic compounds generally present in concentrations of less than 1 mg L¡1), and (iii) pathogenic microorganisms.[3,21,22] Although the source of and the problems derived from leachates are well known, there is little information regarding the differences between leachates generated in a MSWlandfill site and those produced in a MSW-Treatment Plant. The importance of the leachate generated by centralized facilities is sometimes neglected, giving priority to the whole treatment of MSW, the appropriate deposit of rejected materials and the amount of recycled components. Furthermore, the leachate generated in a landfill is usually treated directly in a wastewater treatment plant, which causes consequent problems in the performance of the biological reactor and the accumulation of their metal content into the sludge. The aim of this study was to compare the composition of a leachate generated in a MSW-Treatment Plant (aerobic process) with that produced in an adjacent sealed MSWlandfill site (anaerobic process) and to study the feasibility to treat both leachates using a biological process in a Membrane Biological Reactor (MBR). Furthermore, the effect of seasonal variations (spring, summer, autumn and winter) on the physicochemical properties of the leachates was also studied.
Materials and methods Description of the MSW-treatment plant in Aranda de Duero (Burgos, Spain) The Municipal Solid Waste Treatment Plant (MSW-TP) processes urban wastes produced in a total of 161 small villages around the main town of Aranda de Duero (Burgos, Spain), 41 41’ 53’’ N 03 43’ 02’’ W, approximately 29,000 tonnes year¡1. After a partial segregation at source, mixed MSWs were collected and transported using withdrawal trucks form different transfer places to the MSWTP, according with a centralized scheme of MSW-management (Fig. 1). MSW enters the facility in MSW-collection trucks, and thereafter it is manually sorted and the organic fraction separated on a conveyor belt by the use of a rotary trommel of 5 mm mesh. This fraction is subsequently introduced into composting tunnels, where it performs a 15 days active decomposition step under controlled conditions of humidity, temperature and aeration. After this time it is sent to a covered fermentation shed for another four weeks of aerobic fermentation in windrows, where it is weakly turned and moisturized. The resulting biostabilized material is sieved and refined ( P2 > P1) indicates that the concentration of Cr is higher in P3 than in P2 and, in turn, higher in P2 than in P1. These results are displayed in Figure 2.
Table 1. Physical and chemical parameters. Parameters pH EC (dS m¡1) DM (%) a 60 C Density (g m¡1) COD (mg L¡1) BOD (mg L¡1) COD/BOD TS (mg L¡1) SS (mg L¡1) VS (mg L¡1) C total (mg L¡1) C inorg (mg L¡1) TOC (mg L¡1) N total (mg L¡1) N org (mg L¡1) N-NH4C(mg L¡1) N-NO3¡ C NO2¡ (mg L¡1) PO43¡ (mg L¡1)
P1.1
P2.1
P3.1
P1.2
P2.2
P3.2
7.7 § 0.2 11.7 § 0.2 0.702 § 0.090 0.998 § 0.020 4097 § 1439 200 § 4 20 7005 § 886 1123 § 173 1562 § 245 2354 § 1 1620 § 0 735 § 0 851 § 0 181 § 2 670 § 19 n.d. 26 § 1
7.6 § 0.2 8.6 § 0.2 0.425 § 0.014 0.998 § 0.020 11585 § 998 1260 § 25 9 4236 § 132 2059 § 204 1998 § 218 5400 § 1 1136 § 0 4265 § 0 1445 § 1 680 § 27 765 § 35 n.d. 83 § 2
8.1 § 0.2 54.9 § 1.1 4.593 § 0.616 1.023 § 0.020 16812 § 0 600 § 12 28 46842 § 6581 597 § 36 27854 § 15 11950 § 4 684 § 0 11266 § 0 6805 § 3 783 § 133 6022 § 52 n.d. 83 § 2
7.7 § 0.2 23.8 § 0.5 1.542 § 0.150 0.998 § 0.020 12042 § 1485 300 § 6 40 15496 § 1539 1349 § 154 5150 § 1262 3477 § 2 2200 § 1 1277 § 2 1494 § 1 218 § 47 1276 § 80 n.d. 18 § 0
6.9 § 0.1 36.0 § 0.7 3.098 § 0.079 1.001 § 0.020 40758 § 2008 700 § 14 58 31249 § 739 10171 § 1788 14124 § 241 7685 § 1 1008 § 15 6677 § 16 2853 § 0 591 § 2 2262 § 14 n.d. 82 § 2
8.0 § 0.2 61.2 § 1.2 5.353 § 0.251 1.026 § 0.021 24589 § 1747 440 § 9 56 54775 § 2662 1020 § 52 31695 § 1885 12820 § 2 694 § 0 12127 § 0 7165 § 1 416 § 172 6749 § 160 n.d. 85 § 12
Analytical results for leachates P1, P2 and P3 for samples collected in spring and summer (n.d. under de limit of detection).
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García-L opez et al.
Table 2. Physical and chemical parameters.
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Parameters pH EC (dS m¡1) DM (%) a 60 C Density (g m¡1) COD (mg L¡1) BOD (mg L¡1) COD/BOD TS (mg L¡1) SS (mg L¡1) VS (mg L¡1) C total (mg L¡1) C inorg (mg L¡1) TOC (mg L¡1) N total (mg L¡1) N org (mg L¡1) N-NH4C(mg L¡1) N-NO3¡ C NO2¡ (mg L¡1) PO43¡ (mg L¡1)
P1.3
P2.3
P3.3
P1.4
P2.4
P3.4
7.4 § 0.1 19.9 § 0.4 1.150 § 0.019 0.999 § 0.020 26154 § 523 4230 § 85 6 11524 § 182 1203 § 233 2144 § 48 4591 § 0 1685 § 1 2906 § 0 1181 § 0 444 § 12 737 § 45 n.d. 22 § 1
7.6 § 0.2 24.1 § 0.5 1.805 § 0.012 1.001 § 0.020 25066 § 501 7740 § 155 3 18182 § 150 4234 § 304 6034 § 99 6695 § 2 431 § 1 6264 § 1 1612 § 1 630 § 29 982 § 33 n.d. 87 § 0
7.7 § 0.2 59.7 § 1.2 5.125 § 0.358 1.013 § 0.020 16982 § 340 880 § 18 19 52525 § 3607 577 § 52 29048 § 3181 12320 § 1 706 § 1 11614 § 1 6680 § 0 410 § 132 6270 § 269 n.d. 84 § 2
7.4 § 0.1 20.4 § 0.4 1.586 § 0.023 0.999 § 0.020 21420 § 428 3715 § 74 6 15908 § 252 1755 § 542 6559 § 63 4145 § 232 1625 § 1 2520 § 263 1933 § 14 799 § 907 1134 § 63 0§0 3§0
7.4 § 0.1 18.2 § 0.4 1.807 § 0.208 1.001 § 0.020 37560 § 751 5813 § 116 6 18034 § 2057 11862 § 11515 10059 § 879 7891 § 33 1631 § 1 6260 § 26 3213 § 1 1625 § 53 1588 § 36 3§0 12 § 1
8.0 § 0.2 65.8 § 1.3 2.864 § 0.238 1.025 § 0.021 9538 § 191 715 § 14 13 29339 § 2452 933 § 13 5265 § 2210 11550 § 1 4871 § 1 6679 § 0 9255 § 0 8008 § 44 1247 § 90 9§1 124 § 1
Analytical results for leachates P1, P2 and P3 for samples collected in autumn and winter (n.d. under de limit of detection).
Heavy metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn) The results obtained are as follows: Spring: Cd (P3 > P2 P1), Cr (P3 > P2 > P1), Cu (P3 > P1 > P2), Mn (P2 > P1 > P3), Ni (P3 > P1 P2), Pb (P2 > P3 > P1), Zn (P2 > P1 P3). Summer: Cd (P2 > P3 P1), Cr (P3 > P2 > P1), Cu (P3 > P1 > P2), Mn (P2 > P1 > P3), Ni (P2 > P3 > P1), Pb (P2 > P1 > P3), Zn (P2 > P1 P3). Autumn: Cd (P2 > P1 P3), Cr (P3 > P2 > P1), Cu (P3 > P2 > P1), Mn (P2 > P1 > P3), Ni (P3 > P2 > P1), Pb (P1 > P2 > P3), Zn (P2 > P1 > P3). Winter: Cd (P3 > > P2 > P1), Cr (P3 > P2 > P1), Cu (P3 > P2 > P1), Mn (P2 > P1 > P3), Ni (P2 > P3 > P1), Pb (P3 > P2 > P1), Zn (P2 > P1 > P3). Mean: Cd (P3 > P2 > P1), Cr (P3 > P2 > P1), Cu (P3 > P2 > P1), Mn (P2 > P1 > P3), Ni (P3 > P2 > P1), Pb (P2 > P3 > P1), Zn (P2 > P1 > P3).
The origin and composition of MSWs that produce both leachates are similar, which lead us to hypothesize a
similar concentration of heavy metals in the leachates produced in the MSW-Treatment Plant (MSW-TP) and the MSW-landfill site. Furthermore, as discussed above, the implementation of separate collection, the absence of IW in MSW, etc., the composition of MSW derived to the landfill site is likely to have a higher metal concentration than those of the MSW delivered to the MSW-TP. The main difference between both would be the way in which the waste that generates the leachate is “stored” and the different chemical and biological processes that occur in the MSW-landfill site and in the MSW-TP. Thus, the waste in the MSW-TP is produced in an oxidising environment (active composting phase: fermentation in tunnels; passive phase: fermentation shed), whereas the waste in the landfill site is produced in a reducing environment (lack of oxygen in the mass of residue stored in the landfill: anaerobiosis). However, in contrast to our initial expectations, the concentration of Mn, Pb and Zn in leachates P1 and P2 was higher than in leachate P3. Although, the concentration of the remaining heavy metals (Cd, Cr, Cu and Ni) was higher in P3 than in P2, and higher in P2 than in P1.
Table 3. TS, VS and VS/TS values for leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean values obtained. Spring P1 TS VS VS/TS
P2
Summer P3
7005 4236 46842 1562 1998 27854 22% 47% 59% P3 > P2 > P1
P1
P2
Autumn P3
15496 31249 54775 5150 14124 31695 33% 45% 58% P3 > P2 > P1
P1
P2
Winter P3
11524 18182 52525 2114 6034 29048 18% 33% 55% P3 > P2 > P1
P1
P2
Mean P3
15908 18034 29339 6559 10059 5265 41% 56% 18% P2 > P1 > P3
P1
P2
P3
12483 17925 45870 3846 8054 23466 31% 45% 51% P3 > P2 > P1
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Fig. 2. Heavy metal contents of Cd, Cr, Cu, Mn, Ni and Pb, in leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean values.
Fig. 3. Heavy metal contents of Zn, and other metallic elements Na, K, Ca, Mg and Fe in leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean values.
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The most likely explanation for the higher concentration of Mn, Pb and Zn found in leachates P1 and P2 would be the different chemical reactions that occur in these wastes in the two environments under study, where pH plays a key role. Thus, inside the landfill site, heavy metals are linked to the organic matter (OM) present in the waste, which makes their subsequent separation and leaching much slow and/or difficult. In contrast, in the composting process, leaching of Mn, Pb and Zn is greater despite their apparently lower initial concentration. Thus would explain why leachate P2 presents a 2731%, 425% and 22% higher concentration of Mn, Zn and Pb, respectively, than leachate P3, and why leachate P1 exhibits a 579% and 28% higher concentration of Mn and Zn, respectively, than leachate P3. Other elements (Na, K, Ca, Mg, Fe) can be found in Figure 3. The results obtained are as follows: Spring: Na (P3 > P1 > P2), K (P3 > P1 > P2), Ca (P2 > P1 > P3), Mg (P1 > P2 > P3) and Fe (P3 > P2 > P1). Summer: Na (P3 > P2 > P1), K (P2 > P1 > P3), Ca (P2 > P1 > P3), Mg (P2 > P1 > P3) and Fe (P2 > P3 > P1). Autumn: Na (P3 > P2 > P1), K (P2 > P3 > P1), Ca (P2 > P1 > P3), Mg (P2 > P1 > P3) and Fe (P3 P2 > P1). Winter: Na (P3 > P1 > P2), K (P3 > P1 > P2), Ca (P2 > P1 > P3), Mg (P1 > P2 > P3) and Fe (P2 > P1 > P3). Mean: Na (P3 > P1 P2), K (P3 > P2 P1), Ca (P2 > P1 > P3), Mg (P1 > P2 > P3) and Fe (P2 > P3 > P1).
García-L opez et al. The values for Na and K agree well with the EC values. The main difference between the EC for leachate P3 (60.41 dS m¡1) and those for leachates P1 and P2 (18.95 and 21.73 dS m¡1, respectively) arises due to the different mean Na and K concentration in P3 with respect to P1 (241% and 34% higher for the former, respectively) and P2 (245% and 33% higher for the former, respectively). It may be the case that Na and K form more stable bonds to OM particles in the composting tunnels and fermentation sheds than in the sealed landfill site. The opposite is found for Ca and Mg, both of which are present in higher concentrations in leachates P1 (612% and 565%, respectively) and P2 (2226% and 511%, respectively) than in leachate P3. This can be explained on the basis of the different mean pH values for leachate P3 (7.9) and leachates P1 and P2 (7.6 and 7.4, respectively). Ca and Mg are strongly leached from the landfill site due to anaerobic decomposition of the waste mass. In contrast, in the composting tunnels and fermentation shed, Ca and Mg are more strongly bound to, and stabilised by, OM particles and some proteins and are therefore leached to a lesser extent. Finally, the Fe concentration in all three leachates varies markedly with season and not displayed a clear pattern of variation with the origin of the leachate. Evolution of the chemical properties of the leachates Other parameters (TOC, SS, VS, N-total, N-NH4C, N-organic) can be found in Figure 4. The results obtained are as follows:
Fig. 4. TOC, N-total, N-NH4C, SS, VS and TS in leachates P1, P2 and P3 in spring, summer, autumn, winter and the mean.
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Spring: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P3 > P2 > P1). Summer: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P2 > P3 > P1). Autumn: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P2 > P1 > P3). Winter: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P2 > P3 > P1), N-total (P3 > P2 > P1), N-NH4C (P2 > P3 > P1) and N-organic (P3 > P2 > P1). Mean: TOC (P3 > P2 > P1), SS (P2 > P1 > P3), VS (P3 > P2 > P1), N-total (P3 > P2 > P1), N-NH4C (P3 > P2 > P1) and N-organic (P3 > P2 > P1).
The fact that mean values of COT, N-Total, N-NH4C and N-org for leachate P3 are much higher than those for leachates P1 and P2 is easily explained. Thus, P3 exhibits 78% higher TOC, 228% higher N-total, 173% higher NNH4C and 262% higher N-org values than P2. Furthermore, the TS value is higher for P3 than for P2, and for P2 than for P1. As can be seen from Table 3, a similar situation is found for VS (except for the winter sample), thus agreeing with the potential biogas production capacity of anaerobic digestion. The higher TOC content for P3 is due to the washout of recalcitrant OM, which requires more time to be decomposed by anaerobic than for aerobic processes. The majority of these volatile solids are converted into CH4, CO2, NH3, etc. with time, whereas in bio-oxidative processes part of the carbon remains un-volatilized and is converted into humus. A similar situation is found for nitrification. Thus, as most nitrogen is present in the ammonium form, a longer period of time is required for some of this nitrogen to be converted into nitrate. Furthermore, a significant amount of the N present would be lost by volatilization during the process.
The reason why the SS value is lower for leachate P3 than for leachates P1 and P2 is probably related to the sample collection method. Thus, sample P3 is collected using a small ladle whereas, due to their restricted access, samples P1 and P2 are obtained using a submersible pump. The TS and VS/TS ratio values can be found in Table 3. The results obtained were analysed using an ANOVA with two fixed factors, namely leachate type (three levels, P1, P2 and P3) and season of year when the sample was obtained (four levels, four seasons). Although the differences obtained for Cd, Cu, Pb, K, Fe, C-inorg, C-org were not significant for any leachate type, statistically significant differences with leachate type were obtained for Cr, Mn, Ni, Zn, Na, Ca, Mg, TS, SS, VS, C-total, TOC, Ntotal, N-NH4C and PO43¡ (P < 0.01). The season when the samples were collected was only significant for Pb, Cd, Ni, Mg and N-total (P < 0.01). The overall bivariate Pearson’s correlations coefficients between heavy metals and the other elements in leachates P1, P2 and P3 can be found in Table 4. The degree of bivariate correlation using the Pearson coefficient indicates the degree of correlation between two variables. The main finding of this part of the study was that the presence of metals such as Cd, Cr, Zn and Mn in the leachate was strongly correlated with the of other metals such as Pb, Na, Mn, Ca and Fe, which suppose similar leaching mechanisms besides the different processes affecting the evolution of MSWs in the MSW-TC and in the landfill. Thus, the Cd content in the leachates was highly correlated with the content of Pb (89%) with a significance of 99%. Similarly, Cr was correlated with Na (89%), Zn with Mn, Ca and Fe (83%, 78% and 74%, respectively) and, finally the Mn content of the leachates was correlated to Ca and Fe (74% and 70%, respectively). Use of MBR in leachates depuration Zhao et al.[24] reported that aged refuse reactors have long been used for the cost-effective treatment of landfill
Table 4. Bivariate correlations between heavy metals and other metallic elements in leachates P1, P2 and P3.
[Cu] [Ni] [Cd] [Pb] [Cr] [Zn] [Mn] [Fe] [Ca] [Mg] [K] [Na]
[Cu]
[Ni]
[Cd]
[Pb]
1 0.247 ¡0.138 ¡0.157 0.331* ¡0.195 ¡0.328 ¡0.128 ¡0.268 ¡0.198 0.324 0.464**
1 0.675** 0.596** 0.641** 0.424** 0.113 0.381* 0.302 0.229 0.652** 0.738**
1 0.943** 0.311 0.224 0.075 0.047 0.295 0.723** 0.332* 0.337*
1 0.170 0.251 0.136 0.029 0.379* 0.761** 0.292 0.209
*95% probability. **99% probability.
[Cr]
[Zn]
[Mn]
[Fe]
[Ca]
[Mg]
[K]
1 ¡0.253 1 ¡0.445** 0.910** 1 ¡0.030 0.858** 0.836** 1 ¡0.445** 0.884** 0.861** 0.682** 1 ¡0.377* 0.319 0.279 ¡0.003 0.531** 1 0.400* 0.037 ¡0.268 ¡0.077 0.042 0.149 1 0.946** ¡0.218 ¡0.496** ¡0.067 ¡0.369* ¡0.266 0.613**
[Na]
1
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García-L opez et al.
Table 5. Global performance of the MBR using different mixtures of leachates. Parameters
Heavy metals
Elements
Leachate mixtures
TOC
N total
N-NH4C
Cd
Cu
Ni
Pb
Zn
Cr
Mn
Fe
Na
K
Ca
Mg
LE100P2-LP100P2 LE75P2P3-LP75P2P3 LE50P2P3-LP50P2P3 LE100P1-LP100P1 LE50P1P3-LP50P1P3
80% 91% 79% 98% 100%
51% 57% 11% 38% 82%
30% 35% 13% 8% 83%
58% 52% 42% 23% 45%
58% 40% 21% 28% 47%
98% 92% 26% 42% 86%
46% 71% 21% 13% 59%
97% 96% 88% 77% 88%
81% 94% 70% 69% 98%
98% 96% 88% 77% 68%
93% 95% 83% 96% 99%
18% 27% 20% 0% 78%
29% 16% 19% 23% 58%
91% 94% 84% 78% 73%
21% 42% 36% 23% 13%
Ca
Mg
92% 87% 73% 88% 93%
37% 28% 33% 34% 37%
Table 6. Performance of the ultrafiltrationdevice operating with the MBR effluent at different ratios of leachates. Parameters
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Leachate mixtures
TOC
LE100P2-LP100P2 81% LE75P2P3-LP75P2P3 83% LE50P2P3-LP50P2P3 71% LE100P1-LP100P1 97% LE50P1P3-LP50P1P3 100%
Heavy metals
N total N-NH4C 49% 33% 22% 40% 39%
19% 4% 3% 21% 28%
Elements
Cd
Cu
Ni
Pb
Zn
Cr
57% 36% 45% 37% 85%
66% 15% 95% 75% 51%
99% 86% 19% 72% 76%
42% 57% 39% 23% 55%
97% 92% 87% 90% 93%
86% 87% 82% 89% 78%
leachate. Moreover, the chemical oxygen demand (COD), biological oxygen demand, and ammonia–nitrogen (NH3– N) content can be reduced, thereby making the effluent clear and odorless.[25] Xie et al.[26] constructed aged refuse bioreactors to simulate the landfill leachate degradation process. Their results show that the aged refuse bioreactor could effectively remove leachate pollutants at a hydraulic loading rate of 20 m3 d¡1. However, the aged refuse bioreactor can often be blocked during operation, which could deteriorate the effluent quality. Recently, MBR technology, an advanced biological treatment process that replaces the traditional secondary clarifier of an activated sludge process by a membrane separation unit, has emerged as a promising alternative. The MBR technology has been applied to the treatment of contaminants in both municipal and industrial wastewater.[27,28] MBR technology provides biological treatment with membrane separation.[29,30] The system consists of an aerated water-filled tank containing activated sludge and multiple capillary-form membrane tubes. The pores of ultrafiltration membranes are approximately 20–50 nm in diameter, which effectively retains microorganisms, macromolecules and suspended solids. Microorganisms use the contaminants as nutrients for growth and metabolism. Results from the reatment of the leachates can be found in Tables 5 and 6 for the different leachates and their mixtures. The global performance of the biological process, with and without decantation, and the performance in the membranes were analyzed. The global performance was very high with an important decrease in the TOC contents in all of the cases. In general, this decrease in the contents
Mn
Fe
Na
K
97% 93% 3% 13% 92% 98% 5% 19% 86% 97% 15% 31% 94% 99% 4% 9% 95% 100% 4% 11%
of N-total and N-NH4C in leachate was not as good as the organic content elimination, but level of depuration was important in same cases (82% and 83%, respectively). The reduction in the heavy metal content of leachates was also important. Maximum reductions were reached in Ni, Cr and Mn contents (98%), Zn (97%), Pb (71%), and Cd and Cu (58%). The better performance was obtained with the content of Fe and Ca which reached 99% and 94% of the initial concentration, respectively. In general, the decrease was lower for alkaline metals such as Na, K and Mg contents. The membrane yield in the ultrafiltration process was very high with the TOC, reaching the maximum 100%, and with the concentration of heavy metals Ni, Mn, Zn, Cu, Cr, Cd and Pb in which reductions of 99%, 97%, 97%, 95%, 89%, 85%, 57% were reached for these metals, respectively. With the elements Fe, Ca, Mg, K and Na the maximum amounts in metal reduction were 100%, 93%, 37%, 31% and 15%, respectively.
Conclusions The leachate from the landfill site exhibited a higher TS content than those from the MSW-TP. Furthermore, the percentage of VS with respect to TS was also higher for the landfill site. A similar situation was found for TOC, N-total and N-NH4C. No significant differences in the contents of Cd, Cu, Pb, K, Fe, C-inorg or C-org were found between leachates of different origin. The sampling time significantly affected the concentration of Pb, Cd, Ni, Mg and N-total in leachates (P < 0.01).
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Management of leachate treatment for landfill and composting plant The Mn, Zn and, to a lesser extent, Pb present in MSWs were found to leach more readily in an oxidising (composting process) than in a reducing environment (anaerobic digestion). The presence of certain metals, such as Cd, Cr, Zn and Mn, in the leachate has been found to be strongly correlated with the presence of other metals such as Pb, Na, Mn, Ca and Fe. Usually, a combinations of physical, chemical and biological methods for landfill leachate treatment, is more efficient than using one of these methods separately. In general, the use of a MBR with ultrafiltration is a good tool to treat in a similar way, leachates from MSWTP and landfill. Removal efficiency values from 20% to over of 90% in chemical oxygen demand (COD) were achieved according to leachate characteristics (origin and age), process type and process operational aspects. Nitrification is generally readily achievable, with >95% removal of ammonia reported through the exclusive application of biological techniques to the treatment of both young and old leachates.
[9]
[10]
[11]
[12]
[13]
[14]
[15]
Funding [16]
This work was partially financed by VALORIZA, the commercial firm managing the MSW treatment centre of Aranda de Duero (Burgos, Spain). [17]
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