Influence of alkalinity on the stabilization of municipal solid waste in anaerobic simulated bioreactor

Four simulated landfill anaerobic bioreactors were performed to investigate the influence of alkalinity on the anaerobic treatment of municipal solid waste (MSW). Leachate was recirculated in all the four reactors. One reactor was operated without alkalinization. The other three were operated under alkaline conditions. Na(2)CO(3), NaHCO(3) and NaOH were added to leachate in the second, third and fourth reactor, respectively. Experimental results showed that CO(3)(2-) and HCO(3)(-) addition had a more pronounced effect on MSW stabilization while the effect of addition of OH(-) was weak. The concentration of COD, BOD(5), total nitrogen (TN), ammonium nitrogen (NH(4)(+)-N) and nitrate nitrogen (NO(3)(-)-N), etc. in leachate significantly reduced in four reactors. The removal efficiencies were 90.56%, 92.21%, 92.74% and 90.29% for COD, 66.45%, 72.38%, 68.62% and 68.44% for NO(3)(-)-N, and 96.5%, 98.75%, 97.75% and 98% for NO(2)(-)-N in the control, Na(2)CO(3), NaHCO(3) and OH(-) added reactors, respectively. The final BOD(5)/COD was 0.262, 0.104, 0.124, and 0.143, and pH was 7.13, 7.28, 7.42, and 7.24 for control, Na(2)CO(3) added, NaHCO(3) added, and OH(-) added reactor, respectively. Therefore, alkalinity addition had positive effect on the stabilization of MSW.     

Co-landfilling of pretreated waste: disposal and management strategies at lab-scale

The present paper deals with the possible advantages that can be obtained by co-landfilling of municipal solid waste organic fraction (MSWOF) and bottom ash (BA) from the incineration of municipal solid waste. In particular, the aim of the research hereby presented is to check the effect exerted by different disposal (mixed or layered) and management strategies (anaerobic or semiaerobic conditions) for landfills in which MSWOF and BA are co-disposed. Three lab-scale reactors were set-up: the reactor A with mixed BA and MSWOF in anaerobic conditions, the reactor B with mixed BA and MSWOF in semiaerobic conditions, the reactor C with layered BA and MSWOF in anaerobic conditions. The results obtained showed that the aeration at the beginning of the experimental period for about 60 days led to a more rapid biodegradation of the organic matter and to an improved leachate quality in terms of both organic load and nitrogen content. Also a significant increase in the settling rate was observed at the end of the aeration phase. Therefore, the aerobic management can be advised as the most available strategy providing a more rapid biological and mechanical stabilization of the bulk waste. Otherwise, the disposal strategy did not exert any significant effect on the leachate characteristics; however, the layered configuration may be adopted in order to accelerate the main settlements.     

Impact of various leachate recirculation regimes on municipal solid waste degradation

Landfilled municipal solid waste can be treated by introducing leachate into the waste matrix. Increasing attention is being given to landfill leachate recirculation as a means for in situ leachate treatment and landfill stabilization. Landfills with leachate recirculation may be operated as municipal solid waste bioreactor treatment system rather than as a conventional waste dumping sites. In order to study the impact of various leachate recirculation regimes on municipal solid waste degradation, two landfill-simulating reactors, one with leachate recycle and one without, were constructed and placed at a constant room temperature (34 degrees C). Both reactors were filled with a municipal solid waste mixture representing the typical solid waste composition determined for the city of Istanbul. For the purpose of this experiment, leachate recirculation volume and frequency were changed periodically. This research showed that increased frequency of leachate recirculation accelerates the stabilization rate of waste matrix. About 2l of recirculated leachate and four times per week recirculation strategy were found to provide the highest degree of waste stabilization. Additionally, this research confirmed that leachate recirculation is a very feasible way for in situ leachate treatment.     

Metal concentrations of simulated aerobic and anaerobic pilot scale landfill reactors

Leachate and solid waste samples from aerobic and anaerobic simulated landfill reactors operated with and without leachate recirculation were characterized in terms of metals such as Fe, Ca, K, Na, Cd, Cr, Cu, Pb, Ni, and Zn. Metal concentrations of aerobic landfill reactor leachate samples are always below the regulation limits. The higher concentrations in anaerobic landfill leachate samples decreased to regulation limits after the landfill becomes methanogenic. The effect of leachate recirculation is determined in anaerobic landfills more clearly than aerobic landfills. Metal precipitation resulted in a decrease in leachate metal content and an increase in solid waste metal content as expected. Result of the study show that the metal content of landfill leachate samples is not a major concern for both aerobic and anaerobic landfills.     

Biodegradation of 4-CP in an activated sludge reactor: effects of biosurfactant and the sludge age

The biosurfactant's effect on the biodegradation of 4-chlorophenol (4-CP) in the existence of glucose was researched under the circumstances of using unacclimated culture and various sludge ages. The removal efficiencies of chemical oxygen demand (COD) and 4-CP, the growth of biomass and specific substrate removal rates were examined under various operating conditions. When 150 mg/l concentration of 4-CP was applied, glucose and 4-CP degraded in the same period in the unacclimated bioreactors where biosurfactant was added. Nevertheless, the COD removal in the control reactor noticeably decreased and when compared with reactors which biosurfactant was added, a longer period was needed for the degradation of 4-CP in this reactor. While the complete removal of 4-CP in the control reactor eventuated on the 14th day, in the reactor which 2xcritical micelle concentration (CMC) was added the complete removal of 4-CP eventuated on the end of the 1st day. These results showed that addition of biosurfactant reduced the transient time before the steady-state. COD and 4-CP removal performances were improved by increasing the sludge age. No difference in system performance was observed at high sludge ages in the absence and presence of biosurfactant. However, the performance of the system in the presence of biosurfactant was satisfactory even at low sludge ages. That is, the system should be operated either at high sludge ages (>15 days) in the absence of biosurfactant or at low sludge ages (<15 days) in the presence of surfactants.     

Biostabilization assessment of MSW co-disposed with MSWI fly ash in anaerobic bioreactors

Municipal solid waste incinerator (MSWI) fly ash has been examined for possible use as landfill interim cover. For this aim, three anaerobic bioreactors, 1.2m high and 0.2m in diameter, were used to assess the co-digestion or co-disposal performance of MSW and MSWI fly ash. Two bioreactors contained ratios of 10 and 20 g fly ash per liter of MSW (or 0.2 and 0.4 g g(-1) VS, that is, 0.2 and 0.4 g fly ash per gram volatile solids (VS) of MSW). The remaining bioreactor was used as control, without fly ash addition. The results showed that gas production rate was enhanced by the appropriate addition of MSWI fly ash, with a rate of approximately 6.5l day(-1)kg(-1)VS at peak production in the ash-added bioreactors, compared to approximately 4l day(-1)kg(-1)VS in control. Conductivity, alkali metals and VS in leachate were higher in the fly ash-added bioreactors compared to control. The results show that MSW decomposition was maintained throughout at near-neutral pH and might be improved by release of alkali and trace metals from fly ash. Heavy metals exerted no inhibitory effect on MSW digestion in all three bioreactors. These phenomena indicate that proper amounts of MSWI fly ash, co-disposed or co-digested with MSW, could facilitate bacterial activity, digestion efficiency and gas production rates.     

In situ distributions and characteristics of heavy metals in full-scale landfill layers

The leachate from methanogenic landfill normally contains low concentrations of heavy metals. Little samples had ever been collected from the full-scale landfill piles owing to technical difficulty for well drilling. We drilled two wells in Hangzhou Tianziling landfill, 20 m and 32 m in depth each, and collected solid samples of waste age of 1-4 years from both wells. The total amounts, the sequentially extracted amounts, and the chemical binding forms of heavy metals of the samples collected at different depths were measured. With the correlation between leachate production amount and the yearly rainfall amount, the leached ratio of the heavy metals were estimated only 0.13%, 1.8%, 0.15%, and 0.19% of Cu, Cd, Pb, and Zn, respectively. The heavy metals amounts in the main compositions of MSW, like glass, food waste, paper, coal cinders, were measured using fresh MSW samples. Afterward, the contents of heavy metals initially landfilled were estimated. A positive correlation was noted between the measured and the estimated initial contents of heavy metals, indicating that the low migration of heavy metals in landfill layers. However, among the metals investigated, Zn has shown better mobility inside landfill layers. Acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) were measured for all collected samples with optimal reaction conditions identified to yield nearly perfect sulfide recovery as follows: 100 g wet samples, 80 mL min(-1) N(2) flow rate, reaction time of 150 min. The SEM/AVS ratios ranged 25-45, indicating that the AVS was insufficient to immobilize the SEM. Sequential extraction using six-fraction scheme revealed that the sum of exchangeable and the avid soluble fractions of heavy metals follow: Zn>Cd>Cu, Ni, Pb>Cr. The insoluble fraction of heavy metals in MSW was high, for instance, over 80% for Cr and Pb high insoluble fractions of heavy metals in the landfilled MSW and the sorption capability of the methanogenic landfill layers should be responsible to the low concentrations of heavy metals found in leachate.     

The metal-leaching and acid-neutralizing capacity of MSW incinerator ash co-disposed with MSW in landfill sites

Municipal solid waste (MSW) incinerator (MSWI) bottom ash and fly ash were used as landfill cover or were co-disposed with MSW to measure their potential metal-releasing and acid-neutralizing capacity (ANC) in landfill sites. Five lysimeters (height 1.2m, diameter 0.2m), simulating landfill conditions, were used in the experiment. Four contained either bottom ash (BA) or fly ash (FA) with BA:MSW ratios of 100 and 200 g L(-1) and FA:MSW ratios of 10 and 20 g L(-1), and the fifth was the control, which contained no ash. The lysimeters were arranged so as to contain four layers, with BA or FA placed on top of MSW within each layer. Each lysimeter was recirculated with 100mL leachate using peristaltic pumps, and 100mL of the leachate was collected weekly to measure the soluble metal concentrations. The results showed that the concentrations of soluble alkali metals measured in the leachate were in the order Ca>K>Na>Mg. In addition, the concentrations of soluble alkali metals of Ca and K collected from the lysimeters containing FA were found to be higher than the concentrations from the lysimeters containing BA. The concentrations of heavy metals (Cd, Cr, Cu, Ni, and Zn) were found to be <1 mg L(-1) except for Pb, which reached 2 mg L(-1). These results suggest that for alkali metals there might be an ANC consistent with the results of an acid titration curve, which would provide suitable conditions for anaerobic digestion of the MSW in the landfill. Furthermore, heavy metals and trace metals were found in concentrations, which were too low to exert inhibitory effects on anaerobic digestion, and thus they could serve as micronutrients to exert beneficial rather than detrimental effects on landfill biostabilization.     

Mass-balance estimation of heavy metals and selected anions at a landfill receiving MSWI bottom ash and mixed construction wastes

An estimation of the heavy metal and anion mass-balance was made for municipal solid waste incinerator bottom ash deposited at a construction and industrial waste landfill. The mass-balance was found by comparing the content of metals and anions in the landfill leachate to the metal and anion content in the deposited bottom ash. The discharge of heavy metals ranged from 0.001% for Pb to 0.55% for Cr, which is approximately at the same level as in regular municipal solid waste (MSW) landfills. Landfilled organic material and silicates from construction waste might have contributed to the retention of metals. Chloride, and to a lesser extent sulphate, appeared to be readily released from the landfill. It was estimated that a mass corresponding to 80% of the Cl- and 18% of the SO(4)2- in the bottom ash was discharged annually. Low retention, especially of chloride, may lead to a rapid decline in the discharge of this ion in the future when the landfilling of bottom ash is discontinued.     

Nitrogen removal in the bioreactor landfill system with intermittent aeration at the top of landfilled waste

High ammonia concentration of recycled landfill leachate makes it very difficult to treat. In this work, a vertical aerobic/anoxic/anaerobic lab-scale bioreactor landfill system, which was constructed by intermittent aeration at the top of landfilled waste, as a bioreactor for in situ nitrogen removal was investigated during waste stabilization. Intermittent aeration at the top of landfilled waste might stimulate the growth of nitrifying bacteria and denitrifying bacteria in the top and middle layers of waste. The nitrifying bacteria population for the landfill bioreactor with intermittent aeration system reached between 10(6) and 10(8) cells/dry g waste, although it decreased 2 orders of magnitude on day 30, due to the inhibitory effect of the acid environment and high organic matter in the landfilled waste. The denitrifying bacteria population increased by between 4 and 13 orders of magnitude compared with conventional anaerobic landfilled waste layers. Leachate NO(3)(-)-N concentration was very low in both two experimental landfill reactors. After 105 days operation, leachate NH(4)(+)-N and TN concentrations for the landfill reactor with intermittent aeration system dropped to 186 and 289 mg/l, respectively, while they were still kept above 1000 mg/l for the landfill reactor without intermittent aerobic system. In addition, there is an increase in the rate of waste stabilization as well as an increase of 12% in the total waste settlement for the landfill reactor with intermittent aeration system.     

Pharmaceutical compound content of municipal solid waste

The occurrence and fate of pharmaceuticals in landfills has been largely neglected. Once discarded in municipal solid waste (MSW), pharmaceuticals within a landfill may undergo degradation, adsorption, or enter the leachate and eventually exit the landfill. The active pharmaceutical ingredient (API) concentration of MSW was predicted using available statistics on medication usage and directly measured by a MSW composition study. Estimation calculations resulted in a potential concentration of APIs from 7.4 to 45 mg/kg of MSW, varying with the percentage of dispensed medications assumed to become unused. Direct measurement resulted in the collection of 22 APIs comprising a total of 22,910 mg. This resulted in a final concentration of 8.1 mg/kg within MSW. Additionally, 45 empty medication containers were collected which potentially contained 33 differing APIs upon disposal.     

Solubility of heavy metals added to MSW

This paper aims to investigate the six heavy metal levels (Cd, Cr, Cu, Pb, Ni and Zn) in municipal solid waste (MSW) at different pHs. It intends to provide the baseline information of metals solubility in MSW co-disposed or co-digested with MSW incinerator ashes in landfill or anaerobic bioreactors or heavy metals contaminated in anaerobic digesters. One milliliter (equal to 1mg) of each metal was added to the 100ml MSW and the batch reactor test was carried out. The results showed that higher HNO3 and NaOH were consumed at extreme pH of 1 and 13 compared to those from pH 2 to 11 due to the comparably higher buffer capacity. Pb was found to have the least soluble level, highest metal adsorption (%) and highest partitioning Kd (lg(-1)) between pH 3 and 12. In contrast, Ni showed the highest soluble level, lowest metal adsorption (%) and lowest Kd (lg(-1)) between pH 4 and 12. Except Ni and Cr, other four metals seemed to show the amphibious properties as comparative higher solubility was found in the acidic and basic conditions.     

Use of Fenton reaction for the treatment of leachate from composting of different wastes

The oxidation of leachate coming from the composting of two organic wastes (wastewater sludge and organic fraction of municipal solid wastes) using the Fenton's reagent was studied using different ratios [Fe(2+)]/[COD](0) and maintaining a ratio [H(2)O(2)]/[COD](0) equal to 1. The optimal conditions for Fenton reaction were found at a ratio [Fe(2+)]/[COD](0) equal to 0.1. Both leachates were significantly oxidized under these conditions in terms of COD removal (77 and 75% for leachate from wastewater sludge composting and leachate from organic fraction of municipal solid wastes, respectively) and BOD(5) removal (90 and 98% for leachate from wastewater sludge composting and leachate from organic fraction of municipal solid wastes, respectively). Fenton's reagent was found to oxidize preferably biodegradable organic matter of leachate. In consequence, a decrease in the biodegradability of leachates was observed after Fenton treatment for both leachates. Nevertheless, Fenton reaction proved to be a feasible technique for the oxidation of the leachate under study, and it can be considered a suitable treatment for this type of wastewaters.     

MSW fly ash stabilized with coal ash for geotechnical application

The solidification and stabilization of municipal solid waste (MSW) fly ash for the purpose of minimizing the geo-environmental impact caused by toxic heavy metals as well as ensuring engineering safety (strength and soaking durability) are experimentally evaluated. The mixtures of MSW fly ash stabilized with cement and fluidized bed combustion coal fly ash (FCA) were used for unconfined compressive strength tests, leachate tests, and soaking tests. The behavior of soluble salts contained in the MSW fly ash significantly affects strength development, soaking durability, and the hardening reaction of the stabilized MSW fly ash mixtures. The cement stabilization of the MSW fly ash does not have enough effect on strength development and soaking durability. The addition of cement only contributes to the containment of heavy metals due to the high level of alkalinity. When using FCA as a stabilizing agent for MSW fly ash, the mixture exhibits high strength and durability. However, the Cd leachate cannot be prevented in the early stages of curing. Using a combination of cement and FCA as a MSW fly ash stabilizer can attain high strength, high soaking durability, and the containment of heavy metals. The stabilized MSW fly ash with cement and FCA can be practically applied to embankments.     

The leaching of lead from lead-based paint in landfill environments

Lead leaching from lead-based paint (LBP) was examined using standardized laboratory protocols and tests with leachate from actual and simulated landfill environments. Two different LBP samples were tested; leaching solutions included leachates from three municipal solid waste (MSW) landfills and three construction and demolition (C&D) debris landfills. The toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP) were also performed. Lead concentrations were many times higher using the TCLP compared to the SPLP and the landfill leachates. No significant difference (alpha=0.05) was observed in leached lead concentrations from the MSW landfill and C&D debris landfill leachates. The impact of other building materials present in LBP debris on lead leaching was examined by testing mixtures of LBP (2%) and different building materials (98%; steel, wood, drywall, concrete). The type of substrate present impacted lead leaching results, with concrete demonstrating the most dramatic impact; the lowest lead concentrations were measured in the presence of concrete under both TCLP and SPLP extractions.     

Effect of MSW source-classified collection on the emission of PCDDs/Fs and heavy metals from incineration in China

Municipal solid waste (MSW) source-classified collection represents a change in MSW management in China and other developing countries. Comparative experiments were performed to evaluate the effect of a newly established MSW source-classified collection system on the emission of PCDDs/Fs (polychlorinated dibenzo-p-dioxins and dibenzofurans) and heavy metals (HMs) from a full-scale incinerator in China. As a result of presorting and dewatering, the chlorine level, heavy metal and water content were lower, but heat value was higher in the source-classified MSW (classified MSW) as compared with the conventionally mixed collected MSW (mixed MSW). The generation of PCDDs/Fs in flue gas from the classified MSW incineration was 9.28 ng I-TEQ/Nm(3), only 69.4% of that from the mixed MSW incineration, and the final emission of PCDDs/Fs was only 0.12 ng I-TEQ/Nm(3), although activated carbon injection was reduced by 20%. The level of PCDDs/Fs in fly ash from the bag filter was 0.27 ng I-TEQ/g. These results indicated that the source-classified collection with pretreatment could improve the characteristics of MSW for incineration, and significantly decrease formation of PCDDs/Fs in MSW incineration. Furthermore, distributions of HMs such as Cd, Pb, Cu, Zn, Cr, As, Ni, Hg in bottom ash and fly ash were investigated to assess the need for treatment of residual ash.     

Anaerobic biogranulation in a hybrid reactor treating phenolic waste

Granulation was examined in four similar anaerobic hybrid reactors 15.5L volume (with an effective volume of 13.5L) during the treatment of synthetic coal wastewater at the mesophilic temperature of 27+/-5 degrees C. The hybrid reactors are a combination of UASB unit at the lower part and an anaerobic filter at the upper end. Synthetic wastewater with an average chemical oxygen demand (COD) of 2,240 mg/L, phenolics concentration of 752 mg/L and a mixture of volatile fatty acids was fed to three hybrid reactors. The fourth reactor, control system, was fed with a wastewater containing sodium acetate and mineral nutrients. Coal waste water contained phenol (490 mg/L); m-, o-, p-cresols (123.0, 58.6, 42 mg/L); 2,4-, 2,5-, 3,4- and 3,5-dimethyl phenols (6.3, 6.3, 4.4 and 21.3mg/L) as major phenolic compounds. A mixture of anaerobic digester sludge and partially granulated sludge (3:1) were used as seed materials for the start up of the reactors. Granules were observed after 45 days of operation of the systems. The granules ranged from 0.4 to 1.2 mm in diameter with good settling characteristics with an SVI of 12 mL/gSS. After granulation, the hybrid reactor performed steadily with phenolics and COD removal efficiencies of 93% and 88%, respectively at volumetric loading rate of 2.24 g COD/Ld and hydraulic retention time of 24 h. The removal efficiencies for phenol and m/p-cresols reached 92% and 93% (corresponding to 450.8 and 153 mg/L), while o-cresol was degraded to 88% (corresponding to 51.04 mg/L). Dimethyl phenols could be removed completely at all the organic loadings and did not contribute much to the residual organics. Biodegradation of o-cresol was obtained in the hybrid-UASB reactors.     

Trace element exposure in the environment from MSW landfill leachate sediments measured by a sequential extraction technique

Dredged leachate sediments from eight MSW landfills were dried and homogenized, and metals sequentially extracted. The concentrations of cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) were found to be similar to those reported for sewage sludge, and generally below the EU limits for use of sludge on agricultural land. Sequential extraction of the samples showed that the largest fractions of the heavy metals were associated with Fe- or Mn-oxides. Cr and Cu were the only metals investigated that were associated with the organic matter in the sediments to any significant extent (2-10% of Cr and 10-28% of Cu). Since the largest fractions of the metals studied were bound to Fe-oxides, and thus had a low mobility, these metals will generally have a low bioavailability under aerobic conditions when present in leachate sediments. This is most likely also valid for particulate matter suspended in MSW landfill leachate and released to the environment, since this is the source of the sediments.     

Hazardous waste generation and management in China: a review

Associated with the rapid economic growth and tremendous industrial prosperity, continues to be the accelerated increase of hazardous waste generation in China. The reported generation of industrial hazardous waste (IHW) was 11.62milliontons in 2005, which accounted for 1.1% of industrial solid waste (ISW) volume. An average of 43.4% of IHW was recycled, 33.0% was stored, 23.0% was securely disposed, and 0.6% was discharged without pollution controlling. By the end of 2004, there were 177 formal treatment and disposal centers for IHW management. The reported quantity of IHW disposed in these centers was only 416,000tons, 65% of which was landfilled, 35% was incinerated. The quantity of waste alkali and acid ranked the first among IHW categories, which accounted for 30.9%. And 39.0% of IHW was generated from the raw chemical materials and chemical products industry sectors. South west China had the maximum generation of IHW, accounted for 40.0%. In addition, it was extrapolated that 740,000tons of medical wastes were generated per year, of which only 10% was soundly managed. The generation of discarded household hazardous waste (HHW) is another important source of hazardous waste. A great proportion of HHW was managed as municipal solid waste (MSW). Hazardous waste pollution controlling has come into being a huge challenge faced to Chinese environmental management.     

In situ heavy metal attenuation in landfills under methanogenic conditions

The purpose of this research was to determine the fate and behavior of heavy metals co-disposed with municipal waste under methanogenic conditions. Two landfill simulating reactors, one with leachate recirculation and the other without, were operated in a constant room temperature at 32 degrees C. These reactors were filled with shredded and compacted municipal solid waste having a typical solid waste composition of Istanbul region. After the onset of the methanogenic conditions, the selected heavy metals including iron, copper, nickel, cadmium and zinc were added according to the amounts suggested for co-disposal under the directives of the Turkish Hazardous Waste Control Regulations. The results of the experiments indicated that about 90% of all heavy metals were precipitated from the reactors within the first 10 days due to the establishment of highly reducing environment and the formation of sulfide from sulfate reduction which provided heavy metal precipitation. No inhibition to the biological stabilization was observed.