Shaikh Ziauddin Ahammad

Effect of temperature on selenium removal from wastewater by UASB reactors.

The effect of temperature on selenium (Se) removal by upflow anaerobic sludge blanket (UASB) reactors treating selenate and nitrate containing wastewater was investigated by comparing the performance of a thermophilic (55 °C) versus a mesophilic (30 °C) UASB reactor. When only selenate (50 μM) was fed to the UASB reactors (pH 7.3; hydraulic retention time 8 h) with excess electron donor (lactate at 1.38 mM corresponding to an organic loading rate of 0.5 g COD L(-1) d(-1)), the thermophilic UASB reactor achieved a higher total Se removal efficiency (94.4 ± 2.4%) than the mesophilic UASB reactor (82.0 ± 3.8%). When 5000 μM nitrate was further added to the influent, total Se removal was again better under thermophilic (70.1 ± 6.6%) when compared to mesophilic (43.6 ± 8.8%) conditions. The higher total effluent Se concentration in the mesophilic UASB reactor was due to the higher concentrations of biogenic elemental Se nanoparticles (BioSeNPs). The shape of the BioSeNPs observed in both UASB reactors was different: nanospheres and nanorods, respectively, in the mesophilic and thermophilic UASB reactors. Microbial community analysis showed the presence of selenate respirers as well as denitrifying microorganisms.

Feasibility study on anaerobic biodegradation of azo dye reactive orange 16

Anaerobic digestion of textile azo-dyes is very effective and widely used since it is cost-effective and energy efficient. The present study deals with the anaerobic degradation of reactive orange 16 (RO 16, an azo-dye) using mixed microbial culture. 80 mL each of three different concentrations of RO 16 (100, 200 and 300 ppm) were taken in 150 mL serum vials containing 20 mL of mixed microbial culture and studied periodically. HPLC and UV data revealed that more than 90% of the color was removed within the very first week of the reactor startup. A high COD removal efficiency (≥80%) was achieved after the steady state. Methane and VFAs were produced, and monitored by Gas chromatography. The pH of the medium was slightly acidic favoring methanogenic activity. The diversity of the microbial community was studied by denaturing gradient gel electrophoresis (DGGE) of the polymerase chain reaction (PCR) amplified products of the bacterial and archeal 16S rRNA and the results showed the presence of significant population of acetogens as well as methanogens in the reactor. Quantitative real time PCR (qPCR) was used for the quantitative analysis of some major genera. This study showed that strategic operation of the anaerobic digester can be a viable option for effective decolorization of a complex substrate resulting in energy (biogas) generation.

Rational immobilization of methanogens in high cell density bioreactors

Production of hydrogen sulphide by sulphate reducing bacteria (SRB) is a serious problem in anaerobic wastewater treatment, because it causes corrosion and reduces the value of methane in the biogas produced. The surface and adhesion characteristics of SRB as measured through the zeta potential are different from those of methanogens. We therefore tested the hypothesis that by choosing a carrier material with the proper surface characteristics (zeta potential) it should be possible to selectively immobilize methanogens while excluding SRB. In a series of batch tests with different support materials complete elimination of SRB was obtained on supports made of nylon, a result in line with our original hypothesis. Maximum preferential immobilization of methanogens was obtained at a temperature of 37 °C with media containing volatile fatty acids (VFA) as the carbon source. Preferential immobilization of methanogens was achieved in an anaerobic fluidized bed reactor (AFBR) with nylon granules as support and in an anaerobic rotating biological contactor (ARBC) with an acrylic disc as support. H2S-free biogas containing 63% and 38% methane were obtained from the AFBR and ARBC, respectively.

Anaerobic-aerobic sequencing bioreactors improve energy efficiency for treatment of personal care product industry wastes

Personal care product (PCP) industry liquid wastes contain shampoo residues, which are usually treated by aerobic activated sludge (AS). Unfortunately, AS is expensive for PCP wastes because of high aeration and energy demands, whereas potentially energy-positive anaerobic designs cannot meet effluent targets. Therefore, combined anaerobic-aerobic systems may be the best solution. Seven treatment systems were assessed in terms of energy and treatment performance for shampoo wastes, including one aerobic, three anaerobic (HUASB, AHR and AnCSTR) and three anaerobic-aerobic reactor designs. COD removals were highest in the HUASB-aerobic (87.9 ± 0.4%) and AHR-aerobic (86.8±0.5%) systems, which used 69.2% and 62.5% less energy than aerobic AS. However, actual methane production rates were low relative to theoretical in the UASB and AHR units (∼10% methane/COD removed) compared with the AnCSTR unit (∼70%). Anaerobic-aerobic sequence reactors show promise for treating shampoo wastes, but optimal designs depend upon whether methane production or COD removal is most important to operations.

Improving the cyanide toxicity tolerance of anaerobic reactor: Microbial interactions and toxin reduction

Anaerobic biological treatment of high organics containing wastewater is amongst the preferred treatment options but poor tolerance to toxins makes its use prohibitive. In this study, efforts have been made to understand the key parameters for developing anaerobic reactor, resilient to cyanide toxicity. A laboratory scale anaerobic batch reactor was set up to treat cyanide containing wastewater. The reactor was inoculated with anaerobic sludge obtained from a wastewater treatment plant and fresh cow dung in the ratio of 3:1. The focus was on acclimatization and development of cyanide-degrading biomass and to understand the toxic effects of cyanide on the dynamic equilibrium between various microbial groups. The sludge exposed to cyanide was found to have higher bacterial diversity than the control. It was observed that certain hydrogenotrophic methanogens and bacterial groups were able to grow and produce methane in the presence of cyanide. Also, it was found that hydrogen utilizing methanogens were more cyanide tolerant than acetate utilizing methanogens. So, effluents from various industries like electroplating, coke oven plant, petroleum refining, explosive manufacturing, and pesticides industries which are having high concentrations of cyanide can be treated by favoring the growth of the tolerant microbes in the reactors. It will provide much better treatment efficiency by overcoming the inhibitory effects of cyanide to certain extent.

Low-energy treatment of colourant wastes using sponge biofilters for the personal care product industry

Four trickling biofilter designs were assessed as low-energy alternatives to aerobic activated sludge (AS) for the treatment of personal care product industry wastes. The designs included partially submerged packed-media and sponge reactors with and without active aeration. Partial submergence was used to reduce active aeration needs. Simulated colourant wastes (up to COD=12,480 mg/L, TN=128 mg/L) were treated for 201 days, including wastes with elevated oxidant levels. COD and TN removal efficiencies were always >79% and >30% (even without aeration). However, aerated sponge reactors consistently had the highest removal efficiencies, especially for TN (∼60%), and were most tolerant of elevated oxidants. This study shows sponge biofilters have great potential for treating colourant wastes because they achieve high treatment efficiencies and reduce energy use by >40% relative to AS systems.

Feasibility tests for treating shampoo and hair colorant wastewaters using anaerobic processes.

Wastes from the personal care product (PCP) industry are often high in biodegradable carbon, which makes them amenable to aerobic biological treatment, although process costs are usually high due to aeration inefficiencies, high electricity demand and production of large amounts of sludge. As such, anaerobic treatment technologies are being considered to lower net energy costs by reducing air use and increasing methane production. To assess the amenability of PCP wastes to anaerobic treatment, methane yields and rates were quantified in different anaerobic reactors treating typical PCP wastes, including wastes from shampoo and hair colorant products. Overall, shampoo wastes were more amenable to methanogenesis with almost double the methane yields compared with colour wastes. To assess relevant microbial guilds, qPCR was performed on reactor biomass samples. Methanosaetaceae abundances were always significantly higher than Methanosarcinaceae and Methanomicrobiales abundances (P < 0.05), and did not differ significantly between waste types. Although colour wastes were less amenable to anaerobic treatment than shampoo wastes, differences cannot be explained by relative microbial abundances and probably result from the presence of inhibiting compounds in hair colorants (e.g., oxidants) at higher levels. Results showed that anaerobic technologies have great potential for treating PCP wastes, but additional work is needed to establish the basis of elevated methane yields and inhibition, especially when colorant wastes are present.

Performance comparison of secondary and tertiary treatment systems for treating antibiotic resistance

Rapid emergence of antibiotic resistance (AR) in developing countries is posing a greater health risk and increasing the global disease burden. AR proliferation mediated by treated/untreated discharges from sewage treatment plants (STPs) is a prime public health concern. Efficient sewage treatment is among our key defenses against the dissemination of infectious diseases. The present study aims to estimate the efficiency of aerobic [activated sludge process (ASP) and modified trickling filter (MTF)] and anaerobic reactors (anaerobic flow-through reactor) along with the three disinfection techniques (UV, ozone and chlorination) in reducing ARB and ARGs present in the domestic sewage. The three treatment systems were operated at different HRTs for 1 year and their performances in terms of treatment of conventional and emerging pollutants (ARB and ARGs) were assessed. The results indicated higher removal of ARB and ARGs in aerobic reactors compared to anaerobic reactor. Treatment studies in various bioreactors showed that the use of MTF along with UV/Ozone was superior to ASP and anaerobic flow-through reactor in reducing both the conventional and emerging pollutants. However, higher reduction of the pollutants was observed at higher HRTs. Though complete removal of coliforms and ARB was observed by treating the wastewater using MTF followed by UV or ozone but substantial levels of ARGs were observed in the effluent. Therefore, different advanced and effective treatment technologies such as filtration (RO), use of zero valent iron, TiO2 photocatalysis and other strong oxidizing agents which can ensure complete removal of ARGs along with ARB need to be evaluated. Though addition of these units will increase the treatment cost, but the increased cost would be negligible compared to the present disease burden of AR.

Effect of electrode surface properties on enhanced electron transfer activity in microbial fuel cells

The influence of electrode surface chemistry over biofilm growth was evaluated for photo‐bioelectrocatalytic fuel cell. A consortium of photosynthetic bacteria was grown onto different electrodes designed with polyethylenimine (PEI) and multiwall carbon nanotubes as hydrophilic and hydrophobic modifier, respectively. The designed electrodes were loaded with 0.08, 0.17, and 0.33 μg/cm2 of PEI to change the hydrophilicity. However, 0.56, 0.72, and 0.83 mg/cm2 of multiwall carbon nanotubes were used to alter the hydrophobicity of the electrodes. The surface chemistry of electrode and bio‐interaction was evaluated as a function of contact angle and biofilm formation. The results were compared with those obtained with a carbon paper electrode. The contact angle on the untreated electrode (carbon paper) was 118°, whereas for hydrophobic and hydrophilic electrodes, the maximum and minimum contact angles were 170° and 0°, respectively. Interestingly, the maximum biofilm growth (0.2275 g, wet basis) was observed on highly hydrophobic surface; however, the maximum electrochemical performance (246 mV) was shown by the most hydrophilic electrode surface. PEI‐based electrode with good biofilm formation showed comparatively higher electrogenic activity.

Energy-efficient stirred-tank photobioreactors for simultaneous carbon capture and municipal wastewater treatment

Algal based wastewater treatment (WWT) technologies are attracting renewed attention because they couple energy-efficient sustainable treatment with carbon capture, and reduce the carbon footprint of the process. A low-cost energy-efficient mixed microalgal culture-based pilot WWT system, coupled with carbon dioxide (CO2) sequestration, was investigated. The 21 L stirred-tank photobioreactors (STPBR) used light-emitting diodes as the light source, resulting in substantially reduced operational costs. The STPBR were operated at average optimal light intensity of 582.7 μmol.s(-1).m(-2), treating synthetic municipal wastewater containing approximately 250, 90 and 10 mg.L(-1) of soluble chemical oxygen demand (SCOD), ammonium (NH4-N), and phosphate, respectively. The STPBR were maintained for 64 days without oxygen supplementation, but had a supply of CO2 (25 mL.min(-1), 25% v/v in N2). Relatively high SCOD removal efficiency (>70%) was achieved in all STPBR. Low operational cost was achieved by eliminating the need for mechanical aeration, with microalgal photosynthesis providing all oxygenation. The STPBR achieved an energy saving of up to 95%, compared to the conventional AS system. This study demonstrates that microalgal photobioreactors can provide effective WWT and carbon capture, simultaneously, in a system with potential for scaling-up to municipal WWT plants.