Anaerobic fermentation of organic solid wastes: volatile fatty acid production and separation

Anaerobic fermentation of organic municipal solid waste was investigated using a leach-bed reactor (LBR) to assess the volatile fatty acid (VFA) production efficiency. The leachate recycle rate in the LBR affected the VFA composition of the leachate. A six-fold increase in the recycle rate resulted in an increase of the acetic acid fraction of leachate from 24.7 to 43.0%. The separation of VFAs via leachate replacement resulted in higher total VFA production. VFA separation from synthetic VFA mix and leachate of a fermented organic waste was assessed via a counter-current flow polytetrafluoroethylene (PTFE) membrane contactor. Acetic and propionic acid permeation fluxes of 13.12 and 14.21 g/m(2).h were obtained at low feed pH values when a synthetic VFA mix was used as a feed solution. The highest selectivity was obtained for caproic acid compared to that of other VFAs when synthetic VFA mix or leachate was used as a feed solution. High pH values and the presence of suspended solids in the leachate adversely affected the permeation rate.

Acidogenic fermentation of municipal solid waste and its application to bio-electricity production via microbial fuel cells (MfCs)

Acidogenic fermentation of organic municipal solid waste (MSW) and the bio-electricity production potential from its volatile fatty acid (VFA)-rich leachate using an air-cathode microbial fuel cell (MFC) was investigated in this study. The acidogenic fermentation of 2 kg of MSW has been carried out in a 6 L anaerobic leach-bed reactor (LBR) under mesophilic conditions (30 degrees C). Total production of 92 g VFA expressed as chemical oxygen demand (COD) in 3 L leachate mainly containing acetic, propionic, butyric, and valeric acids has been achieved with manual leachate recirculation and without pH control in 74 days of incubation. Leachate collected on day 32 was used as a feed to an air-cathode MFC after being diluted and supplemented with NaCl or NaHCO3. The maximum power density in the diluted leachate was only 5.9 W/m3, but reached up to 8.6 W/m3 upon the addition of 7 mmol/L NaCl. Increase in coulombic efficiency from 6 to 22% was also observed as a result of NaCl supplementation. On the other hand, NaHCO3 addition did not improve the power output.

Significance of acetogenic H2 consumption in dark fermentation and effectiveness of pH

Two identical thermophilic H(2) fermenters (R1 and R2) were operated at different pH levels between 4.7 and 5.7. In R1, several unexpected and severe drops in H(2) yield inversely proportional to increase in acetate production were experienced at pH 5.5 and 5.7. In contrast, R2 operated at pH 5 and 4.7 performed more stable H(2) production mainly through butyrate fermentation. Although the H(2) partial pressure (>50 kPa) was far above the favorable values, acetate was produced as well as butyrate in all pH levels tested. To determine whether some portion of the acetate is produced through another pathway such as autotrophic synthesis via H(2) dependent reduction of CO(2) or not, batch dissolved H(2) consumption rate tests were performed at pH 5.0, 5.5 and 6. The specific H(2) consumption rate was 488(+/-49) micromol/gVSS.hr at pH 6 and slightly higher than at pH 5 and 5.5. The results of continuous and batch experiments revealed that acetogenic H(2) consumption is more favorable at pH levels above 5.5 and is one of the reasons of instabilities in dark fermentative H(2) production.

Comparison of long-term performances and final microbial compositions of anaerobic reactors treating landfill leachate

Laboratory scale anaerobic upflow filter, sludge blanket and hybrid bed reactors were operated for 860 days in the treatment of high ammonia landfill leachate. Organic loading was gradually increased from 1.3 to 23.5 kg COD/m3 day in the start-up period and then fluctuated according to the COD concentration of raw leachate. To prevent free ammonia inhibition, influent pH was reduced to 4.5 after Day 181 and consequently COD removal efficiencies above 80% were achieved in all reactors. However, the anaerobic filter and hybrid bed reactor were generally found slightly more efficient and stable than the UASB reactor. In addition to conventional anaerobic reactor control parameters, the complementary techniques of denaturing gradient gel electrophoresis (DGGE), cloning and fluorescent in situ hybridization (FISH) were used to identify and compare the microbial profiles in the reactors at Day 830. Molecular analyses revealed that acetoclastic Methanosaeta species were prevalent in all reactors and configuration did not have an impact on microbial diversity in the long-term.

Identification of prevalent microbial communities in a municipal solid waste landfill

To identify the microbial communities in Istanbul, Odayeri Municipal Solid Waste Landfill, leachate samples were collected from different sections at different stabilization phases. In identification of microbial communities in leachate samples, molecular techniques such as FISH, DGGE and cloning based on 16S rRNA and mcrA genes were used. As the chemical and microbiological compositions of the samples were compared, obvious correlations were found between the stability of the landfill section and abundance of active methanogens. On the other hand, there were considerable differences between acidogenic and mature leachate samples in DGGE profiles of archaeal and bacterial 16S rRNA genes. Moreover, in acidogenic leachate samples having BOD5/COD ratio of about 0.5 acetate utilizing Methanosarcina and Methanosaeta species were intensively detected in FISH. Although only very few H2-utilizing methanogens were identified with FISH analysis, most of the clones isolated from mature leachate samples clustered within H2-utilizing Methanobacteriales and Methanomicrobiales according to phylogenetic analysis of 16S rRNA and mcrA clones, respectively.

Community changes during start-up in methanogenic bioreactors exposed to increasing levels of ammonia

To investigate the methanogenic population dynamics during the start-up under gradually increasing free ammonia levels, five mesophilic UASB reactors seeded with different sludges were operated for 140 days. Changes in the methanogenic community investigated by using 16S rDNA/rRNA based molecular methods such as denaturing gradient gel electrophoresis (DGGE), fluorescent in-situ hybridization (FISH), cloning and DNA sequencing. Free ammonia nitrogen (FAN) in the reactors was gradually increased from 50 to 130 mg l(-1) by increasing total ammonia nitrogen (TAN) from 1000 to 2500 mg l(-1) in the feed and keeping reactor pH at 7.7 in the active zone. Even at highest FAN level, COD and VFA removal efficiencies above 90 and 98% were obtained, respectively. However, Methanosaeta-related species mainly prevailing in seed sludges were substituted for Methanosarcina as the abundant methanogens although reactor performances were almost comparable and constant.

Investigation of variations in microbial diversity in anaerobic reactors treating landfill leachate

A young landfill leachate containing elevated total ammonia concentrations frequently as high as 2,700 mg/l was anaerobically treated for 1,015 days in two different laboratory-scale anaerobic reactors configured as sludge blanket and hybrid bed. In this paper, the last 265 days of this long-term anaerobic treatability study are presented. Effects of high ammonia concentrations on reactor performances were correlated to the variations in microbial diversity by identifying the dominant microorganisms with FISH (fluorescent in-situ hybridization), cloning, DGGE (denaturing gradient gel electrophoresis) and morphological analysis. The results have indicated that the high ammonia landfill leachate can be treated successfully by using either an UASB or a hybrid bed reactor if temporary pH adjustments in the reactor influents are made when high ammonia concentrations are experienced. Consequently, COD removal efficiency is independent of microbial diversity and reactor configuration and it depends on the biodegradable portion of the leachate. Under this circumstance, stability of the reactors with low levels of acetate was supported by the abundance of Methanosaeta population. In both of the reactors, some populations of Methanobacteriaceae were also detected while other methanogenic species were virtually absent. However, after the termination of pH adjustment at Day 860, reactors immediately became unstable due to the sudden increase in free ammonia concentration up to 400 mg/l. COD removal efficiency decreased to 42% in the hybrid bed and to 48% in the UASB reactor. The durations of inhibitions were not long enough to severely deteriorate the massive Methanosaeta cells; therefore, many of them were again identified after two free ammonia inhibitions. However, subsequently, long filamentous morphologies of Methanosaeta cells shifted to shorter filaments and they lost their aggregating property.

Toxicity assessment on combined biological treatment of pharmaceutical industry effluents

This paper describes the wastewater characterization and aerobic/anaerobic treatability (oxygen uptake rate and biogas production measurement) of chemical-synthesis based pharmaceutical industry effluents in a nearby baker's yeast industry treatment plant. Preliminary experiments by the industry had indicated strong anaerobic toxicity. On the other hand, aerobic treatability was also uncertain due to complexity and unknown composition of the wastewater. The work in this study has indicated that the effluents of the pharmaceutical industry can be treated without toxicity in the aerobic stage of the treatment plant. Methanogenic activity tests with anaerobic sludge from the anaerobic treatment stage of the wastewater treatment plant and acetate as substrate have confirmed the strong toxicity, while showing that 30 min aeration or coagulation with an alum dose of 300 mg/l is sufficient for reducing the toxicity almost completely. Powdered activated carbon, lime and ferric chloride (100-1,000 mg/l) had no effect on reduction of the toxicity. Consequently, the pharmaceutical industry was recommended to treat its effluents in the anaerobic stage of the nearby baker's yeast industry wastewater treatment plan at which there will be no VOC emission and toxicity problem, provided that pretreatment is done.

Characterization and anaerobic treatment of the sanitary landfill leachate in Istanbul

In this study, characterization and anaerobic treatability of leachate from Komurcuoda Sanitary Landfill located on the Asian part of Istanbul were investigated. Time based fluctuations in characteristics of leachate were monitored for an 8 month period. Samples were taken from a 200 m3 holding tank located at the lowest elevation of the landfill. COD concentrations have ranged between 18,800 and 47,800 mg/l while BOD5 between 6820 and 38,500 mg/L. COD and BOD5 values were higher in summer and lower in winter due to dilution by precipitation. On the other hand, it was quite interesting that such a dilution effect was not observed for ammonia. The highest ammonia concentration, 2690 mg/L was in November 1998. BOD5/COD ratio was larger than 0.7 for most samples indicating high biodegradability, and acidic phase of decomposition in the landfill. For anaerobic treatability, three different reactors, namely an upflow anaerobic sludge bed reactor, an anaerobic upflow filter and a hybrid bed reactor, were used. The anaerobic reactors were operated for more than 230 days and were continuing operation when this paper was prepared. Organic loading was increased gradually from 1.3 kg COD/m3.day to 8.2 kg COD/m3.day while hydraulic retention time was reduced from 2.4 days to 2.0 days. All the reactors showed similar performances against organic loadings with efficiencies between 80% and 90%. However the reactors have experienced high ammonia concentrations several times throughout the experimental period, and showed different inhibition levels. Anaerobic filter was the least affected reactor while UASB was the most. Hybrid bed reactor has exhibited a similar performance to anaerobic filter although not to the same degree.