Srikanth Mutnuri

Biodegradation of crude oil by Pseudomonas aeruginosa and Escherichia fergusonii isolated from the Goan coast.

Petroleum hydrocarbons are major pollutants of the marine environment. Bioremediation is a promising approach for treating such contaminated environments. The present study aims at isolating naturally occurring bacteria from the coast of Goa, India and to study their hydrocarbonoclastic capacity. Pseudomonas aeruginosa and Escherichia fergusonii were isolated from a crude oil-contaminated sediment sample using diesel oil as the sole carbon source. The capability of the enriched culture to degrade crude oil was estimated using microcosm studies under saline conditions. Based on GC-MS analysis, the culture was found to degrade n-alkanes at a higher rate compared to polyaromatic hydrocarbons. It was also found that the culture degraded alkylated polyaromatic hydrocarbons much less than unalkylated ones. Alkanes ranging from C12 to C33 were highly degraded compared to n-C34. This study shows bioremediation of crude oil in saline (3% NaCl) conditions by naturally existing bacteria isolated from the marine environment.

Anaerobic co-digestion of sewage sludge and food waste:

Anaerobic co-digestion of organic matter improves digester operating characteristics and its performance. In the present work, food waste was collected from the institute cafeteria. Two types of sludge (before centrifuge and after centrifuge) were collected from the fluidised bed reactor of the institute treating sewage wastewater. Food waste and sludge were studied for their physico–chemical characteristics, such as pH, chemical oxygen demand, total solids, volatile solids, ammoniacal nitrogen, and total nitrogen. A biomethane potential assay was carried out to find out the optimum mixing ratio of food waste and sludge for anaerobic co-digestion. Results indicated that food waste mixed with sludge in the ratio of 1:2 produced the maximum biogas of 823 ml gVS−1 (21 days) with an average methane content of 60%. Batch studies were conducted in 5 L lab-glass reactors at a mesophilic temperature. The effect of different substrate loading rates on biogas production was investigated. The mixing ratio of food waste and sludge was 1:2. A loading rate of 1 gVS L d−1 gave the maximum biogas production of 742 ml g−1 VS L d−1 with a methane content of 50%, followed by 2 gVS L d−1 with biogas of 539 ml g−1 VS L d−1. Microbial diversity of the reactor during fed batch studies was investigated by terminal restriction fragment length polymorphism. A pilot-scale co-digestion of food waste and sludge (before centrifuge) indicated the process stability of anaerobic digestion.

Isolation of hydrocarbonoclastic bacteria from bilge oil contaminated water

Two bacterial strains, i.e. Pseudomonas mendocina and Ochrobactrum sp. were isolated from bilge oil contaminated water of Mormugao harbour, Goa, India and grown in a culture medium with hexadecane as the sole carbon source. Pseudomonas mendocina was used in further studies as it was the dominant strain. This strain effectively degraded tetradecane, hexadecane and octadecane leaving a residual concentration of about 73 %, 54 % and 40 % respectively in 120 h. Sequence analysis of the dominant bands from the denaturing gradient gel electrophoresis profiles revealed the differences between the genera of bilge oil contaminated sea water and its enrichment culture on hexadecane indicating a shift in community structure based on the type of substrate available. Pseudomonas mendocina amplified for the following catabolic genes namely C23O, nid and ndo. Based on the catabolic gene study the potential of the bacterial strain isolated, i.e. Pseudomonas mendocina seems to be interesting as it will be able to degrade polyaromatic hydrocarbons as well. Physicochemical properties of Pseudomonas mendocina indicates production of exopolysaccharides based on the value of its isoelectric point.

Biochemical Methane Potential of Agro Wastes

The focus of our work is on anaerobic digestion of locally available agro wastes like coconut oil cake, cashew apple waste, and grass from lawn cuttings. The most productive agro waste, in terms of methane yield, was coconut oil cake and grass. The results showed that the initial volatile solids concentration significantly affected the biogas production. The methane yield from coconut oil cake was found to be 383 ml CH4/g VS and 277 ml CH4/g VS added at 4 and 4.5 g VS/l. In case of grass the biogas production increased with increasing VS concentrations with methane yield of 199, 250, 256, 284, and 332 ml CH4/g VS at 3, 3.5, 4, 4.5, and 5.0 g VS/l. For cashew apple waste single-stage fermentation inhibited biogas production. However, phase separation showed methane yield of 60.7 ml CH4/g VS and 64.6 ml CH4/g VS at 3.5 and 4.0 g VS/l, respectively. The anaerobic biodegradability of coconut oil cake was evaluated in fed batch mode in a 5 L anaerobic reactor at 4 g VS/L per batch, and the maximum methane yield was found to be 320 ml CH4/g VS.

Pretreatment of cottage cheese to enhance biogas production.

This study evaluated the possibility of pretreating selected solid fraction of an anaerobic digester treating food waste to lower the hydraulic retention time and increase the methane production. The study investigated the effect of different pretreatments (thermal, chemical, thermochemical and enzymatic) for enhanced methane production from cottage cheese. The most effective pretreatments were thermal and enzymatic. Highest solubilisation of COD was observed in thermal pretreatment, followed by thermochemical. In single enzyme systems, lipase at low concentration gave significantly higher methane yield than for the experiments without enzyme additions. The highest lipase dosages decreased methane yield from cottage cheese. However, in case of protease enzyme an increase in concentration of the enzyme showed higher methane yield. In the case of mixed enzyme systems, pretreatment at 1 : 2 ratio of lipase : protease showed higher methane production in comparison with 1 : 1 and 2 : 1 ratios. Methane production potentials for different pretreatments were as follows: thermal 357 mL/g VS, chemical 293 mL/g VS, and thermochemical 441 mL/g VS. The average methane yield from single enzyme systems was 335 mL/g VS for lipase and 328 mL/g VS for protease. Methane potentials for mixed enzyme ratios were 330, 360, and 339 mL/g VS for 1 : 1, 1 : 2, and 2 : 1 lipase : protease, respectively.

Effect of caffeine and saponin on anaerobic digestion of food waste

Food waste is the single largest component of the waste stream by weight. In the present work, we attempted to study the effect of caffeine and saponin on anaerobic fermentation of food waste to examine their potential influence on biogas production at 8% total solids (TS) content. Addition of caffeine at 50, 100, and 150 ppm to the food waste on the first day resulted in biogas production in 24 hours which normally comes on 4th day. The maximum biogas production of 408.5 ml/g TS was found at 100 ppm caffeine whereas 50 ppm and 150 ppm caffeine produced 359 ml and 336 ml in comparison with the control which showed 182 ml/g TS. This is the first study of effect of caffeine as stimulants in anaerobic environments. Addition of saponin had no beneficial effect; on the other hand, it inhibited the biogas production at 50, 100 and 150 ppm.

Biodegradation of aliphatic hydrocarbons in the presence of hydroxy cucurbit[6]uril

Aliphatic hydrocarbons are one of the major environmental pollutants with reduced bioavailability. The present study focuses on the effect of hydroxy cucurbit[6]uril on the bioavailability of hydrocarbons. A bacterial consortium was used for biodegradation studies under saline and non-saline conditions. Based on denaturing gradient gel electrophoresis results it was found that the consortium under saline conditions had two different strains. The experiment was conducted in microcosms with tetradecane, hexadecane, octadecane and mixture of the mentioned hydrocarbons as the sole carbon source. The residual hydrocarbon was quantified using gas chromatography every 24h. It was found that biodegradation of tetradecane and hexadecane, as individual carbon source increased in the presence of hydroxy CB[6], probably due to the increase in their bioavailability. In case of octadecane this did not happen. Bioavailability of all three aliphatic hydrocarbons was increased when provided as a mixture to the consortium under saline conditions.

Effect of rhamnolipid on biodegradation of hydrocarbons in non-aqueous-phase liquid (NAPL)

ABSTRACT Aliphatic and aromatic hydrocarbons are environmental pollutants of serious concern. Their bioavailability is the major limiting factor that makes the bioremediation process slow. Therefore, the present study focuses on biodegradation of non-aqueous-phase liquids (NAPL) by a halophilic consortium (Pseudomonas aeruginosa and Escherichia fergusonii) in presence of rhamnolipid as well as a rhamnolipid-producing Pseudomonas aeruginosa AMB AS7. The study was performed in microcosms, and the residual hydrocarbons after degradation were estimated by gas chromatography. It was found that the degradation of hydrocarbons in NAPL was more in presence of rhamnolipid in comparison with their biotic controls. However, among NAPL, the degradation of phenanthrene (37.5%) and octadecane (47.8%) was found to be more by co-culture of halophilic consortium and rhamnolipid-producing P. aeruginosa AMB AS7. Denaturing gradient gel electrophoresis was performed to determine the viability of different bacterial strains (halophilic and rhamnolipid-producing bacterial strain). Besides, the results also revealed that during NAPL degradation, the cell surface hydrophobicity (CSH) of halophilic consortium increased from 9.12% to 69.55% when added with 100 mg/L of rhamnolipid, whereas CSH of rhamnolipid-producing P. aeruginosa AMB AS7 was constant at 31.9%, even though it produced about 271.8 mg/L of rhamnolipid.

Horizontal gene transfer versus biostimulation: A strategy for bioremediation in Goa

Bioaugmentation, Biostimulation and Horizontal gene transfer (HGT) of catabolic genes have been proven for their role in bioremediation of hydrocarbons. It also has been proved that selection of either biostimulation or bioremediation varies for every contaminated site. The reliability of HGT compared to biostimulation and bioremediation was not tested. The present study focuses on reliability of biostimulatiion, bioaugmentation and HGT during biodegradation of Diesel oil and Non aqueous phase liquids (NAPL). Pseudomonas aeruginosa (AEBBITS1) having alkB and NDO genes was used for bioaugmentation and the experiment was conducted using seawater as medium. Based on Gas chromatography results diesel was found to be degraded to 100% in both presence and absence of AEBBITS1. Denturing gradient gel electrophoresis result showed same pattern in presence and absence of AEBBITS1 indicating no HGT. NAPL degradation was found to be more by Biostimulated Bioaugmentation compared to biostimulation and bioaugmentation alone. This proves that biostimulated bioaugmentation is better strategy for oil contamination (tarabll) in Velsao beach, Goa.

Sanitation of blackwater via sequential wetland and electrochemical treatment

The discharge of untreated septage is a major health hazard in countries that lack sewer systems and centralized sewage treatment. Small-scale, point-source treatment units are needed for water treatment and disinfection due to the distributed nature of this discharge, i.e., from single households or community toilets. In this study, a high-rate-wetland coupled with an electrochemical system was developed and demonstrated to treat septage at full scale. The full-scale wetland on average removed 79 ± 2% chemical oxygen demand (COD), 30 ± 5% total Kjeldahl nitrogen (TKN), 58 ± 4% total ammoniacal nitrogen (TAN), and 78 ± 4% ortho-phosphate. Pathogens such as coliforms were not fully removed after passage through the wetland. Therefore, the wetland effluent was subsequently treated with an electrochemical cell with a cation exchange membrane where the effluent first passed through the anodic chamber. This lead to in situ chlorine or other oxidant production under acidifying conditions. Upon a residence time of at least 6 h of this anodic effluent in a buffer tank, the fluid was sent through the cathodic chamber where pH neutralization occurred. Overall, the combined system removed 89 ± 1% COD, 36 ± 5% TKN, 70 ± 2% TAN, and 87 ± 2% ortho-phosphate. An average 5-log unit reduction in coliform was observed. The energy input for the integrated system was on average 16 ± 3 kWh/m3, and 11 kWh/m3 under optimal conditions. Further research is required to optimize the system in terms of stability and energy consumption.Artificial wetlands: Two heads are better than oneWhere constructed wetlands are unable to remove pathogens from wastewater, an electrochemical cell could step in to tackle the challenge. Artificial wetlands can treat domestic wastewater outside of centralized facilities—making them particularly important in countries where safe wastewater transport is difficult—but the efficiency of pathogen removal varies greatly from site to site. A team led by Srikanth Mutnuri at the Institute of Technology and Science in Goa, India, now couple a constructed wetland with a vertical subsurface flow, able to remove organic matter and nutrients from waste, with an electrochemical cell designed to remove pathogens. The cell contains an anode chamber where acidic pH and oxidative species disinfect the effluent, effectively reducing the coliform count where the wetland couldn’t. Optimizing the stability and energy consumption of the system are the crucial next steps.