C. Visvanathan

Membrane Separation Bioreactors for Wastewater Treatment

With continuing depletion of fresh water resources, focus has shifted more toward water recovery, reuse, and recycling, which require an extension of conventional wastewater treatment technologies. Downstream external factors like stricter compliance requirements for wastewater discharge, rising treatment costs, and spatial constraints necessitate renewed investigation of alternative technologies. Coupled with biological treatment processes, membrane technology has gained considerable attention due to its wide range of applicability and the performance characteristics of membrane systems that have been established by various investigations and innovations during the last decade. This article summarizes research efforts and presents a review of the how and why of their development and applications. The focus is on appraising and comparing technologies on the basis of their relative merits and demerits. Additional facts and figures, especially regarding process parameters and effluent quality, are used to evaluate primary findings on these technologies. Key factors such as loading rates, retention time, cross-flow velocities, membrane types, membrane fouling, and backwashing, etc. are some of the aspects covered. Membrane applications in various aerobic and anaerobic schemes are discussed at length. However, the emphasis is on the use of membranes as a solid/liquid separator, a key in achieving desired effluent quality. Further, technology development directions and possibilities are also explored. The review concludes with an economic assessment of the technologies because one of the key technology selection criteria is financial viability.

Bio-energy recovery from high-solid organic substrates by dry anaerobic bio-conversion processes: a review

Dry anaerobic bio-conversion (D-AnBioC) of high-solid organic substrates (OS) is considered as a sustainable option for waste management practices in different parts of the world. The basic technology is well implemented, but the improvements are still under way in terms of optimization and pre- and post-treatments of the feed and end-products, respectively. The purpose of this review is mainly to: (1) provide existing knowledge and research advances in D-AnBioC systems to treat high-solid OS; (2) identify major issues involved in bioreactor designing; (3) present factors influencing the bio-conversion efficiency; (4) discuss the microbiology of system operation; (5) provide examples of existing commercial-scale plants; (6) discuss energy and economics requirements. From the detailed literature review, it is clear that the characteristics of OS are the major factors governing the overall process and economics. It shows that not all OS are profitably recycled using D-AnBioC systems. Compared to single-stage continuous systems, batch systems under a multi-stage configuration appears to be economically feasible, however, it must be noted that the available data sets are still inconclusive. Also, limited information is available on green house gas mitigation and restoration of nutrients from the digested residue during post-treatment schemes. A summary at the end presents important research gaps of D-AnBioC system to direct future research.

Effect of organic loading rate on VFA production, organic matter removal and microbial activity of a two-stage thermophilic anaerobic membrane bioreactor.

This study focused on the VFA (volatile fatty acid) profile variation with organic loading rate (OLR) of a two stage thermophilic anaerobic membrane bioreactor (TAnMBR). The two stage TAnMBR treating high strength molasses-based synthetic wastewater was operated under a side-stream partial sedimentation mode at 55°C. Reactor performances were studied at different OLR ranging from 5 to 12 kg COD m(-3) d(-1). Operational performance of TAnMBR was monitored by assessing biological activity, organic removal efficiency, and VFA. The major intermediate products of anaerobic digestion were identified as acetate, propionate, iso-butyrate, n-butyrate and valerate. Among them acetate and n-butyrate were identified as the most abundant components. Increase of OLR changes the predominant VFA type from acetic acid to n-butyric acid and the total VFA concentration was increased with increased OLR. Moreover, increased OLR increased organic removal efficiency up to second loading rate and dropped in third loading rate while biological activity was increased continuously.

Performance of suspended and attached growth MBR systems in treating high strength synthetic wastewater.

The performance of laboratory-scale attached growth (AG) and suspended growth (SG) membrane bioreactors (MBRs) was evaluated in treating synthetic wastewater simulating high strength domestic wastewater. This study investigated the influence of sponge suspended carriers in AG-MBR system, occupying 15% reactor volume, on the removal of chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), and compared it to that of SG-MBR. Results showed that the removal efficiencies of COD, TN and TP in AG-MBR were 98%, 89% and 58%, respectively as compared to 98%, 74% and 38%, respectively in SG-MBR. Improved TN removal in AG-MBR systems was primarily based on simultaneous nitrification and denitrification (SND) process. These results infer that the presence of small bio-particles having higher microbial activity and the growth of complex biomass captured within the suspended sponge carriers resulted in improved TN and TP removal in AG-MBR.

Effect of C/N ratio and ammonia-N accumulation in a pilot-scale thermophilic dry anaerobic digester.

The effect of ammonia-N accumulation in a dry anaerobic digestion was studied effectively using pilot-scale thermophilic reactor. Two simulations were prepared to attain C/N ratio 27 and C/N ratio 32 using bio-degradable feedstocks such as food waste, fruit and vegetable waste, green waste and paper waste. Organic loading rates and digestate recirculation rates were varied during different time intervals and the performance was evaluated using parameters like pH, VFA, Alkalinity, ammonia-N and biogas yield. Results showed that the simulation with C/N ratio 32 had about 30% less ammonia in digestate as compared to that with C/N ratio 27. The system performed well up to organic loading rate (OLR) 7-10 kgVS/m(3)d and retention time up to 19 days, with surplus energy production of 50-73%. Moreover, a free ammonia accumulation/inhibition effect was documented and methods to overcome the adverse effects were discussed.

Assessment of heavy metal contamination and its mobilization from municipal solid waste open dumping site

Influence of heavy metals was investigated by conducting various tests on the samples collected from Nonthaburi dumpsite in Thailand. The heavy metal concentration in the solid waste and its mobility potential based on its binding forms was studied. The sequential extraction method was used to determine the binding forms of metals. From the analysis, Zn was found to be highest concentrated heavy metal compared to Mn, Cu, Cr, Cd, Pb, Ni and Hg in the solid waste. From the sequential extraction, Mn, Zn and Cd mostly found in reducible form, showed its susceptibility to be leached easily. Cu and Cr were found predominantly in oxidizable form and stable under anaerobic condition. Pb and Ni were present in residual form, which is inert. The estimated individual contamination factor (C(f)(i)), showed Zn with highest affinity to leach. The concentration level of all the heavy metals in the leachate except for Cr was noticed to be below the National effluent standards. Though, indicated to be safe for disposal, its effect in any concentration proved toxic to the plant life from the seed germination toxicity test using synthetic chelate ethylene diamine tetraacetic acid (EDTA).

Studies on colloidal membrane fouling mechanisms in crossflow microfiltration

Abstract In crossflow microfiltration (CFMF), colloids play a significant role in internal and external membrane fouling, which is responsible for the decline in filtration flux. The colloidal membrane fouling mechanisms were studied experimentally using a colloidal silica solution (Ludox HS-40). The results of these experiments were analyzed in terms of membrane resistance and existing membrane filtration model equations. The significance of internal and external colloidal fouling was studied in relation to operational parameters, namely, pressure and volume filtered, and such fouling was compared with total membrane fouling.

Validation of internal controls for extraction and amplification of nucleic acids from enteric viruses in water samples.

ABSTRACT Inhibitors that reduce viral nucleic acid extraction efficiency and interfere with cDNA synthesis and/or polymerase activity affect the molecular detection of viruses in aquatic environments. To overcome these significant problems, we developed a methodology for assessing nucleic acid yields and DNA amplification efficiencies for environmental water samples. This involved adding particles of adenovirus type 5 and murine norovirus and newly developed primer-sharing controls, which are amplified with the same primer pairs and result in the same amplicon sizes as the targets, to these samples. We found that nucleic acid loss during the extraction process, rather than reverse transcription-PCR (RT-PCR) inhibition, more significantly attributed to underestimation of the presence of viral genomes in the environmental water samples tested in this study. Our success rate for satisfactorily amplifying viral RNAs and DNAs by RT-PCR was higher than that for obtaining adequate nucleic acid preparations. We found that inhibitory properties were greatest when we used larger sample volumes. A magnetic silica bead-based RNA extraction method effectively removed inhibitors that interfere with viral nucleic acid extraction and RT-PCR. To our knowledge, this is the first study to assess the inhibitory properties of environmental water samples by using both control virus particles and primer-sharing controls.

Healthcare waste management in Asia

The risks associated with healthcare waste and its management has gained attention across the world in various events, local and international forums and summits. However, the need for proper healthcare waste management has been gaining recognition slowly due to the substantial disease burdens associated with poor practices, including exposure to infectious agents and toxic substances. Despite the magnitude of the problem, practices, capacities and policies in many countries in dealing with healthcare waste disposal, especially developing nations, is inadequate and requires intensification. This paper looks upon aspects to drive improvements to the existing healthcare waste management situation. The paper places recommendation based on a 12 country study reflecting the current status. The paper does not advocate for any complex technology but calls for changes in mindset of all concerned stakeholders and identifies five important aspects for serious consideration. Understanding the role of governments and healthcare facilities, the paper also outlines three key areas for prioritized action for both parties - budget support, developing policies and legislation and technology and knowledge management.

Policy options to promote energy efficient and environmentally sound technologies in small- and medium-scale industries

Abstract The rapid industrialization of Asian developing countries has pushed the need for more energy at the cost of environmental degradation. Though large industries are targeted for energy conservation and pollution prevention, small and medium scale industries (SMI) also contribute to significant pollution. This paper discusses the role of SMI in the economy, its energy consumption and impact on the environment. An overview of the energy and environment policies of China, India, Sri Lanka, the Philippines and Vietnam, and the role of energy efficient and environmentally sound technologies (E3ST) as a viable means to meet these modern challenges in SMI is discussed. The barriers faced in adopting these technologies have been identified and an analysis has been done of the various strategies and policy options available to governments to promote E3ST in SMI. Examples and illustrations of such successful efforts have also been highlighted.