Mathava Kumar

Co-existence of anammox and denitrification for simultaneous nitrogen and carbon removal—Strategies and issues

The discovery of anaerobic ammonium oxidation (anammox) has greatly improved the understanding of the nitrogen cycle. Anammox provides great promise for the removal of nitrogen from wastewater, containing high concentration of ammonium. However, the presence of organic carbon is considered as unfavorable to this autotrophic process, i.e. anammox. Most of the real wastewaters contain both organic carbon and nitrogen. Under this circumstance, several processes have been established primarily for the complete removal of organic carbon. Subsequently, the wastewater containing no or low organic carbon and nitrogen is treated via a variety of nitrogen removal processes. The co-existence of anammox and denitrification could be useful for the simultaneous removal of nitrogen and organic carbon in a single system rather than a sequential chain of treatment. This review addresses the microbiology, strategies, consequences and the future research challenges in the co-existence of anammox and denitrification.

Simultaneous partial nitrification, anaerobic ammonium oxidation and denitrification (SNAD) in a full-scale landfill-leachate treatment plant

The occurrence of simultaneous partial nitrification, anaerobic ammonium oxidation and denitrification (SNAD) observed in a single partially aerated full-scale bioreactor treating landfill-leachate is reported in this paper. At present, the full-scale bioreactor is treating an average leachate flow of 304 m(3)d(-1) with a sludge retention time between 12 and 18d. The average COD, NH(4)(+)-N and NO(3)(-)-N concentrations at the upstream end of the bioreactor, i.e., influent, are 554, 634 and 3 mg L(-1), respectively; whereas no NO(2)(-)-N is detected in the influent. The percentage removals of COD and NH(4)(+)-N in the bioreactor were 28% and 80%, respectively. A nitrogen mass balance approach was adopted to analyze the performance of SNAD in the full-scale bioreactor. The total nitrogen (TN) removal by combined partial nitrification and anaerobic ammonium oxidation is 68% and the heterotrophic denitrification contributes to 8% and 23% of TN and COD removals, respectively. The red granule in the bioreactor was analyzed by using fluorescence in situ hybridization and polymerase chain reaction. The results of both analytical methods confirm the presence of anaerobic ammonium oxidizing bacteria as the predominant species along with other Planctomycete-like bacteria. Overall, the SNAD process offers the simultaneous removals of nitrogen and COD in the wastewater.

Co-composting of green waste and food waste at low C/N ratio

In this study, co-composting of food waste and green waste at low initial carbon to nitrogen (C/N) ratios was investigated using an in-vessel lab-scale composting reactor. The central composite design (CCD) and response surface method (RSM) were applied to obtain the optimal operating conditions over a range of preselected moisture contents (45-75%) and C/N ratios (13.9-19.6). The results indicate that the optimal moisture content for co-composting of food waste and green waste is 60%, and the substrate at a C/N ratio of 19.6 can be decomposed effectively to reduce 33% of total volatile solids (TVS) in 12days. The TVS reduction can be modeled by using a second-order equation with a good fit. In addition, the compost passes the standard germination index of white radish seed indicating that it can be used as soil amendment.

Development of simultaneous partial nitrification, anammox and denitrification (SNAD) process in a sequential batch reactor

Simultaneous partial nitrification, anammox and denitrification (SNAD) process was developed in a sequential batch reactor (SBR) and the influence of hydraulic retention time (HRT) on the SNAD process was investigated. Around 96% NH(4)(+)-N removal and 87% COD removal were observed at 9 d HRT. Marginal decreases in the removal efficiencies were observed when the HRT was reduced to 3d or the loading rate was increased by three times. On the other hand, a drastic decrease in NH(4)(+)-N and COD removals were observed when the DO, pH and temperature were dropped shockingly. The response of the SNAD system towards the shock in substrate loading and operating conditions was evaluated by sensitivity index. Finally, the extent of total nitrogen (TN) removal by partial nitrification with anammox and denitrification was modeled using stoichiometric relationship. Modeling results indicated a TN removal of 85-87% by anammox with partial nitrification and 7-9% by denitrification.

Enrichment and isolation of a mixed bacterial culture for complete mineralization of endosulfan

In the present study, we isolated three novel bacterial species, namely, Staphylococcus sp., Bacillus circulans–I, and Bacillus circulans–II, from contaminated soil collected from the premises of a pesticide manufacturing industry. Batch experiments were conducted using both mixed and pure cultures to assess their potential for the degradation of aqueous endosulfan in aerobic and facultative anaerobic condition. The influence of supplementary carbon (dextrose) source on endosulfan degradation was also examined. After four weeks of incubation, mixed bacterial culture was able to degrade 71.82 ± 0.2% and 76.04 ± 0.2% of endosulfan in aerobic and facultative anaerobic conditions, respectively, with an initial endosulfan concentration of 50 mg l−1. Addition of dextrose to the system amplified the endosulfan degradation efficiency by 13.36 ± 0.6% in aerobic system and 12.33 ± 0.6% in facultative anaerobic system. Pure culture studies were carried out to quantify the degradation potential of these individual species. Among the three species, Staphylococcus sp. utilized more beta endosulfan compared to alpha endosulfan in facultative anaerobic system, whereas Bacillus circulans–I and Bacillus circulans–II utilized more alpha endosulfan compared to beta endosulfan in aerobic system. In any of these degradation studies no known intermediate metabolites of endosulfan were observed.

Anaerobic biotransformation of fluorene and phenanthrene by sulfate-reducing bacteria and identification of biotransformation pathway

In the present study, anaerobic biotransformation of fluorene and phenanthrene by sulfate-reducing bacteria (SRB) was investigated and biotransformation pathways were proposed. SRB was enriched from anaerobic swine wastewater sludge and its abundance was determined by the fluorescence in situ hybridization (FISH) technique. Batch anaerobic biotransformation studies were conducted with fluorene (5 mg L(-1)), phenanthrene (5 mg L(-1)) and a mixture of the two (10 mg L(-1)). After 21d of incubation, 88% of fluorene and 65% of phenanthrene were biotransformed by SRB. In contrast to previous studies, a decrease in biotransformation efficiency was observed in the presence of both fluorene and phenanthrene. Throughout the study, sulfate reduction was coupled with biotransformation of fluorene and phenanthrene. However, no increase in bacterial cell density was observed in the presence of an inhibitor, i.e. molybdate. Identification of metabolites by gas chromatography-mass spectrometry (GC-MS) revealed that fluorene and phenanthrene were biotransformed through a sequence of hydration and hydrolysis reactions followed by decarboxylation with the formation of p-cresol (only in the phenanthrene system) and phenol. The metabolites identified suggest novel biotransformation pathways of fluorene and phenenthrene.

Effect of supplementary carbon addition in the treatment of low C/N high-technology industrial wastewater by MBR

The effect of supplementary carbon addition for the treatment of high-technology industrial wastewater in a membrane bioreactor (MBR) was investigated. The MBR was operated for 302 days under different C/N (BOD(L)/NH(4)(+)-N) ratios, i.e. 0.9-1 to 20 days, 1.6-21 to 42 days, 2.9-43 to 82 days, 3.6-83 to 141 days, 4.8-165 to 233 days and 9.3-240 to 302 days. Irrespective of the C/N ratios investigated, SS and BOD(5) removal efficiencies were above 95% and above 80% COD removal efficiency was observed. In addition, complete nitrification was observed throughout the investigation. However, denitrification and total nitrogen removal efficiencies reached their maximum values at the highest C/N ratio (9.3) investigated. Real-time PCR analysis revealed 10 times higher ammonia oxidizing bacteria to total bacteria ratio under the highest C/N ratio condition (9.3) compared to the low C/N ratio condition (1.6).

Simultaneous sulfate reduction and copper removal by a PVA-immobilized sulfate reducing bacterial culture

The effect of a sulfate reducing bacteria immobilized in polyvinyl alcohol (PVA) on simultaneous sulfate reduction and copper removal was investigated. Batch experiments were designed using central composite design (CCD) with two parameters, i.e. the copper concentration (10-100mg/L), and the quantity of immobilized SRB in culture solution (19-235 mg of VSS/L). Response surface methodology (RSM) was used to model the experimental data, and to identify optimal conditions for the maximum sulfate reduction and copper removal. Under optimum condition, i.e. approximately 138.5mg VSS/L of sulfate reducing bacteria immobilized in PVA, and approximately 51.5mg/L of copper, the maximum sulfate reduction rate was 1.57 d(-1) as based on the first-order kinetic equation. The data demonstrate that immobilizing sulfate reducing bacteria in PVA can enhance copper removal and the resistance of the bacteria towards copper toxicity.

Endosulfan Mineralization by Bacterial Isolates and Possible Degradation Pathway Identification

ABSTRACT A bacterial consortium consists of three bacterial isolates, which rapidly mineralizes endosulfan, was enriched from an endosulfan-processing industrial surface soil. Batch experiments were conducted using bacterial consortium and its pure isolates for their potential degradation of endosulfan and its metabolites, i.e., endosulfan sulfate, endosulfan ether, and endosulfan lactone, in anaerobic condition. Endosulfan degradation was promising with bacterial consortium and pure isolates. Staphylococcus sp. preferably utilized beta endosulfan whereas other two Bacillus strains utilized more alpha endosulfan. The addition of supplementary carbon, i.e., dextrose, stimulated the endosulfan degradation efficiency in both the cases. Degradation of endosulfan ether and endosulfan lactone was promising with Bacillus circulans I and II whereas no endosulfan sulfate was degraded by any of these strains. From the present investigation, it was postulated that endosulfan was mineralized via hydrolysis pathway with the formation of carbenium ions and/or ethylcarboxylates, which later converted into simple hydrocarbons.

Degradation of carbofuran-contaminated water by the Fenton process

In this study, the Fenton process was applied for the degradation of carbofuran from aqueous system. Batch experiments were conducted at two different carbofuran concentrations i.e., 10 and 50 mg/L, and at pH 3. Batch experiments at each carbofuran concentration were designed by central composite design (CCD) with two independent variables i.e. Fe2 + and H2O2. Experimental results indicate that more than 90% of carbofuran removal was observed within 5 mins of Fenton reaction at 5 mg/L of Fe2 + concentration and 100 mg/L of H2O2 concentration. Increases in Fe2 + and/or H2O2 concentrations beyond 5 and 100 mg/L, respectively produced 100% carbofuran removal. Based on the experimental observations, the optimal Fe2 + and H2O2 dosages required for 10 mg/L of aqueous carbofuran removal were estimated as 7.4 and 143 mg/L, respectively. During this study, three carbofuran intermediates such as 7-benzofuranol,2,3,-dihydro-2,2-dimethyl, 7-hydroxy-2,2-dimethyl-benzofuran-3-one and 1,4-Benzene-di-carboxaldehyde were identified using GC/MS analyses.