T.R. Sreekrishnan

Bioleaching of heavy metals from sewage sludge: a review.

During the treatment of sewage, a huge volume of sludge is generated, which is disposed of on land as soil fertilizer/conditioner due to the presence of nitrogen, phosphorus, potassium and other nutrients. However, the presence of toxic heavy metals and other toxic compounds in the sludge restricts its use as a fertilizer. Over the years, bioleaching has been developed as an environmentally friendly and cost-effective technology for the removal of heavy metals from the sludge. The present paper gives an overview of the various bioleaching studies carried out in different modes of operation. The various important aspects such as pathogen destruction, odor reduction and metal recovery from acidic leachate also have been discussed. Further, a detailed discussion was made on the various technical problems associated with the bioleaching process, which need to be addressed while developing the process on a larger scale.

Increased Waterborne blaNDM-1 Resistance Gene Abundances Associated with Seasonal Human Pilgrimages to the Upper Ganges River

Antibiotic resistance (AR) is often rooted in inappropriate antibiotic use, but poor water quality and inadequate sanitation exacerbate the problem, especially in emerging countries. An example is increasing multi-AR due to mobile carbapenemases, such as NDM-1 protein (coded by blaNDM-1 genes), which can produce extreme drug-resistant phenotypes. In 2010, NDM-1 positive isolates and blaNDM-1 genes were detected in surface waters across Delhi and have since been detected across the urban world. However, little is known about blaNDM-1 levels in more pristine locations, such as the headwaters of the Upper Ganges River. This area is of particular interest because it receives massive numbers of visitors during seasonal pilgrimages in May/June, including visitors from urban India. Here we quantified blaNDM-1 abundances, other AR genes (ARG), and coliform bacteria in sediments and water column samples from seven sites in the Rishikesh-Haridwar region of the Upper Ganges and five sites on the Yamuna River in Delhi to contrast blaNDM-1 levels and water quality conditions between season and region. Water quality in the Yamuna was very poor (e.g., anoxia at all sites), and blaNDM-1 abundances were high across sites in water (5.4 ± 0.4 log(blaNDM-1·mL–1); 95% confidence interval) and sediment (6.3 ± 0.7 log(blaNDM-1·mg–1)) samples from both seasons. In contrast, water column blaNDM-1 abundances were very low across all sites in the Upper Ganges in February (2.1 ± 0.6 log(blaNDM-1·mL–1)), and water quality was good (e.g., near saturation oxygen). However, per capita blaNDM-1 levels were 20 times greater in June in the Ganges water column relative to February, and blaNDM-1 levels significantly correlated with fecal coliform levels (r = 0.61; p = 0.007). Given that waste management infrastructure is limited in Rishikesh-Haridwar, data imply blaNDM-1 levels are higher in visitor’s wastes than local residents, which results in seasonally higher blaNDM-1 levels in the river. Pilgrimage areas without adequate waste treatment are possible “hot spots” for AR transmission, and waste treatment must be improved to reduce broader AR dissemination via exposed returning visitors.

Bioleaching of heavy metals from sewage sludge by indigenous iron-oxidizing microorganisms using ammonium ferrous sulfate and ferrous sulfate as energy sources: a comparative study.

The potential of indigenous iron-oxidizing microorganisms enriched at initial neutral pH of the sewage sludge for bioleaching of heavy metals was investigated at initial neutral pH of the sludge using ammonium ferrous sulfate (FAS) and ferrous sulfate (FS) as an energy sources in two different sets of experiments. After 16 days of bioleaching, 56% Cu, 48% Ni, 68% Zn and 42% C were removed from the sludge using ammonium ferrous sulfate as an energy source. On the other hand, 64% Cu, 58% Ni, 76% Zn and 52% Cr were removed using ferrous sulfate. Further, 32% nitrogen and 24% phosphorus were leached from the sludge using ferrous sulfate, whereas only 22% nitrogen and 17% phosphorus were removed using ammonium ferrous sulfate. The BCR sequential extraction study on speciation of metals showed that using ammonium ferrous sulfate and ferrous sulfate, all the metals remained in bioleached sludge as stable form (F4 fraction). The results of the present study indicate that the bioleached sludge would be safer for land application. Also, the fertilizing property was largely conserved in the bioleached sludge using both the substrates.

Effect of operating temperatures on the microbial community profiles in a high cell density hybrid anaerobic bioreactor

Lack of knowledge about the microbial consortia involved in wastewater treatment at different operating temperatures, is a major reason for failure of anaerobic reactors in field applications. Present study was undertaken to correlate performance of hybrid anaerobic reactors operating at different temperatures (37, 45 and 55 °C) to structures of archaeal and bacterial communities involved. Self-immobilized granules were developed in the reactors continuously fed with synthetic wastewater (10,000 mg COD l(-1)) and operated at an organic loading rate of 2.22 kg COD m(-3) day(-1) and hydraulic retention time of 5 days. The reactor operated at 37 °C showed the best performance as well as the most diverse microbial community revealed by PCR-denaturing gradient gel electrophoresis analysis using 16S rRNA gene amplicons. Sequences derived from reactors operating at higher temperatures revealed presence of different methanogens, but lesser diversity caused a drop in COD degradation capability of the system indicating successful operation at low loading conditions.

Effect of sulfur concentration on sludge acidification during the SSDML process

Abstract Heavy metals present in sewage sludges can be leached out, among other processes, by a process using a consortium of sulfur oxidizing bacteria. The metal leaching could be combined with aerobic sludge digestion to result in the Simultaneous Sludge Digestion and Metal Leaching (SSDML) process. A detailed knowledge of the effect of sulfur concentration on the pH variations of the sludge during the process is essential to a complete understanding of the process kinetics. To achieve this objective, SSDML experiments were conducted in Erlenmeyer flasks and 20 1 reactors and the results were analysed. The sludge pH was seen to rise initially, which was attributed to a lag in the activity of sulfur oxidizing bacteria combined with the production of unidentified material, which are basic in their effect on the sludge pH. The lag period was found to depend on (i) the surface area of sulfur available for bacterial attachment and (ii) the number of bacteria present in the sludge capable of initiating bacterial colonies on these surfaces. The rate of change of sludge pH during the lag period was found to depend on the sludge pH itself and the two were related using a second degree polynomial. The specific growth and product formation rates of the sulfur oxidizing bacteria were found to vary linearly with the surface area of sulfur available when the bacterial metabolism was sulfur limited and mathematical relations were developed for the same. The rate constants were evaluated by calculating the instantaneous growth and sulfate formation rates and comparing the resultant change in the sludge pH with experimentally observed values. These equations were used to simulate the sulfate production and pH variations in the sludge for various conditions. The simulation results matched the experimental results very well, confirming the validity of the relations developed.

Effect of seed culture on solid-state bioconversion of wheat straw by phanerochaete chrysosporium for animal feed production

The solid-state bioconversion of wheat straw by Phanerochaete chrysosporium for the production of animal feed was studied. This study was performed based on a central composite experimental design. The conditions of the seed culture most suitable for rapid induction of the ligninolytic activity of the fungus, when the seed culture is subsequently used for solid-state bioconversion of wheat straw, were determined. When the seed culture with an initial pH of 5.8 was grown under agitated conditions at 130 rpm in baffled flasks at 38 degrees C, it was predicted to give lignin degradation of 19.5% and cellulose degradation of 17.8%. A time profile study of the solid-state bioconversion of wheat straw indicated that the highest lignin and lowest cellulose degradation levels occurred on the sixth day of cultivation. The desirability coefficient for this process also passed through a maximum of 0.705 on the sixth day.

Effect of salt concentration and mediators in salt bridge microbial fuel cell for electricity generation from synthetic wastewater.

The aim of this study was to investigate the feasibility of using agar salt bridges for proton transport in Microbial Fuel Cells (MFC). It also tries to elucidate and effect of mediators on electricity production from wastewaters through experimentation using a simulated wastewater. In order to offset the very high cost of proton exchange membrane, salt bridges have been used in dual chamber MFCs. When the concentration of salt was varied in agar salt bridges from 1% to 10%, the volumetric power density changed from 1.71 to 84.99 mW/m3 with a concomitant variation in power density from 0.32 to 16.02 mW/m2. The maximum power density was observed at 5% salt concentration with 10% agar, which was accompanied by 88.41% COD reduction. In the case of methylene blue (0.01 mM) as the electron mediator, the voltage and current generation were 0.551 V and 0.47 mA, respectively. A maximum open circuit voltage of 0.718 V was seen at 0.08 mM methylene blue concentration, whereas maximum power densities of 17.59 mW/m2 and 89.22 mW/m3 were obtained. Different concentrations of neutral red were also tried out as mediators. A maximum open circuit voltage of 0.730 V was seen at 0.01mM neutral red, corresponding to a power density of 12.02 mW/m2 (volumetric power density of 60.97 mW/m3). Biofilm formation on the electrode surface was not observed in the presence of mediators, but was present in the absence of mediators. The results clearly demonstrated the feasibility to use agar salt bridge for proton transport and role of mediators in MFCs to generate electricity.

Removal of various pollutants from wastewater by electrocoagulation using iron and aluminium electrode

The present study deals with removal of various pollutants from a real wastewater by electrocoagulation treatment. Combined wastewater from one of the Delhi industrial areas was collected and treated by electrocoagulation process using iron and aluminium electrodes. Removal of Cr, Zn, Ni and Cu were achieved up to 100, 98.71, 69.22 and 48.08% respectively using aluminium electrode while Cr, Cu, Zn and Ni were removed up to 100, 78.57, 75.48 and 58.68% respectively using iron electrode electrocoagulation. Chemical oxygen demand, total organic carbon, total dissolved solids and sulphate were removed up to 83.94, 46.92, 74.16 and 83.66%, respectively in aluminium electrode electrocoagulation while the same were removed up to 54.83, 77.39, 52.85 and 60.74% respectively in iron electrode electrocoagulation.

Production of methionine by a multi-analogue resistant mutant of Corynebacterium lilium

Multi-analogue resistant mutants of Corynebacterium lilium were developed using UV and N -methyl-N ?-nitro-nitrosoguanidine (NTG) mutagenesis in order to overproduce methionine. Although the methionine yield at each stage of mutation by UV and NTG mutagenesis were comparable, it was observed that the NTG mutants had higher cell growth and glucose utilization rates. From the parent NTG mutant C. lilium E 4 resistant to ethionine, the highest methionine producing strain C. lilium M-128 resistant to 3.5 mg ml � 1 of ethionine, 3.0 mg ml � 1 of norleucine, 3.8 mg ml � 1 of methionine sulphoxide and 3.8 mg ml � 1 of methionine methyl sulphoniumchloride was derived. When C. lilium M-128 was grown under optimised conditions, it produced 2.3 g l � 1 of methionine in a 15 l batch reactor. The maximum cell mass concentration obtained was 17 g l � 1 dry cell weight resulting in a cell yield coefficient of 0.34 g g � 1 . The dissolved oxygen concentration was controlled at 40% saturation by cascade control of the airflow rate and agitation speed. # 2002 Elsevier Science Ltd. All rights reserved.

Changes in microbial communities in a hybrid anaerobic reactor with organic loading rate and temperature

Poor understanding of the response of microbial communities to sudden changes in organic and hydraulic loads is one of the major reasons for the inability to prevent operational instabilities in anaerobic reactors. Effect of changes in hydraulic retention time (HRT) and organic loading rate (OLR) on reactor performance and its anaerobic microbial community were investigated in two anaerobic hybrid reactors operated at 37 and 55 °C. HRT was reduced stepwise, while OLR was increased along with influent chemical oxygen demand at fixed HRT until the performance of reactor deteriorated. The profile of archaeal 16S rRNA gene amplicons, resolved by denaturing gradient gel electrophoresis, reflected system status during disturbances. The more diverse archaeal community in the reactor operated at 37 °C showed better performance than the communities present at 55 °C at higher OLR and shorter HRT, suggesting that higher diversity is indicative of more stable operation of reactors despite organic and hydraulic shocks.