Ajit P. Annachhatre

Biodegradation of chlorinated phenolic compounds

Chlorophenolic compounds are generated from a number of industrial manufacturing processes including pulp and paper manufacture. These compounds are found to be toxic and recalcitrant and hence their discharge into the environment must be regulated. Slow and partial degradation of chlorophenols under aerobic and anaerobic natural environment has been observed. Aerobic biodegradation of chlorophenols proceeds through the formation of catechols while under anaerobic conditions, reductive dehalogenation is the preferred metabolic pathway. Number and position of chlorine substituents on the phenolic ring has influence on the rate and extent of biodegradation of chlorophenols. In engineered systems, acclimatization of biomass to chlorophenols markedly enhances the biodegradation ability by reducing the initial lag phase and by countering inhibition. Partial removal of chlorophenols between 40-60% is usually observed in aerobic and anaerobic processes. Removal can be enhanced by a combination of aerobic and anaerobic operations.

Biological sulfide oxidation in an airlift bioreactor

Biological sulfide oxidation process was investigated in an airlift reactor under oxygen-limited condition (0.2-1.0 mg l(-1)). Reactor start-up was accomplished using seed sludge from activated sludge process treating domestic wastewater. Synthetic wastewater was used as feed. Gradual increase in volumetric sulfide loading rate resulted in increase of elemental sulfur production. At sulfide loading rate of 2.2 kg S m(-3)d(-1), 50% of influent sulfide was converted to elemental sulfur. At maximum volumetric sulfide loading rate of 4.0 kg S m(-3)d(-1), sulfide consumption of 4.3 kg S kg VSS(-1)d(-1) was achieved, and over 93% of sulfide removal was observed. Investigation revealed that up to 90% of sulfide removed was converted to elemental sulfur. Addition of polyaluminium chloride as coagulant was found to be effective for sulfur-particle aggregation.

Organic substrates as electron donors in permeable reactive barriers for removal of heavy metals from acid mine drainage.

This research was conducted to select suitable natural organic substrates as potential carbon sources for use as electron donors for biological sulphate reduction in a permeable reactive barrier (PRB). A number of organic substrates were assessed through batch and continuous column experiments under anaerobic conditions with acid mine drainage (AMD) obtained from an abandoned lignite coal mine. To keep the heavy metal concentration at a constant level, the AMD was supplemented with heavy metals whenever necessary. Under anaerobic conditions, sulphate-reducing bacteria (SRB) converted sulphate into sulphide using the organic substrates as electron donors. The sulphide that was generated precipitated heavy metals as metal sulphides. Organic substrates, which yielded the highest sulphate reduction in batch tests, were selected for continuous column experiments which lasted over 200 days. A mixture of pig-farm wastewater treatment sludge, rice husk and coconut husk chips yielded the best heavy metal (Fe, Cu, Zn and Mn) removal efficiencies of over 90%.

Biological sulfate removal from construction and demolition debris leachate: Effect of bioreactor configuration

Due to the contamination of construction and demolition debris (CDD) by gypsum drywall, especially, its sand fraction (CDD sand, CDDS), the sulfate content in CDDS exceeds the posed limit of the maximum amount of sulfate present in building sand (1.73 g sulfate per kg of sand for the Netherlands). Therefore, the CDDS cannot be reused for construction. The CDDS has to be washed in order to remove most of the impurities and to obtain the right sulfate content, thus generating a leachate, containing high sulfate and calcium concentrations. This study aimed at developing a biological sulfate reduction system for CDDS leachate treatment and compared three different reactor configurations for the sulfate reduction step: the upflow anaerobic sludge blanket (UASB) reactor, inverse fluidized bed (IFB) reactor and gas lift anaerobic membrane bioreactor (GL-AnMBR). This investigation demonstrated that all three systems can be applied for the treatment of CDDS leachate. The highest sulfate removal efficiency of 75-85% was achieved at a hydraulic retention time (HRT) of 15.5h. A high calcium concentration up to 1,000 mg L(-1) did not give any adverse effect on the sulfate removal efficiency of the IFB and GL-AnMBR systems.

Anaerobic co-digestion of cyanide containing cassava pulp with pig manure

Anaerobic co-digestion of cyanide-containing cassava pulp with pig manure was evaluated using laboratory scale mesophilic digester. The digester was operated in a semi-continuous mode with the mixed feedstock having C/N ratio of 35:1. Digester startup was accomplished in 60days with loading of 0.5-1kgVS/m(3)d. Subsequently, the loading to digester was increased step-wise from 2 to 9kgVS/m(3)d. Digester performance was stable at loading between 2 and 6kgVS/m(3)d with an average volatile solid removal and methane yield of 82% and 0.38m(3)/kgVSadded, respectively. However, beyond loading of 7kgVS/m(3)d, solubilization of particulate matter did not take place efficiently. Cyanide present in cassava pulp was successfully degraded indicating that anaerobic sludge in the digester was well acclimatized to cyanide. The results show that cassava pulp can be successfully digested anaerobically with pig manure as co-substrate without any inhibitory effect of cyanide present in the cassava pulp.

Precipitation of heavy metals from coal ash leachate using biogenic hydrogen sulfide generated from FGD gypsum

Investigations were undertaken to utilize flue gas desulfurization (FGD) gypsum for the treatment of leachate from the coal ash (CA) dump sites. Bench-scale investigations consisted of three main steps namely hydrogen sulfide (H(2)S) production by sulfate reducing bacteria (SRB) using sulfate from solubilized FGD gypsum as the electron acceptor, followed by leaching of heavy metals (HMs) from coal bottom ash (CBA) and subsequent precipitation of HMs using biologically produced sulfide. Leaching tests of CBA carried out at acidic pH revealed the existence of several HMs such as Cd, Cr, Hg, Pb, Mn, Cu, Ni and Zn. Molasses was used as the electron donor for the biological sulfate reduction (BSR) process which produced sulfide rich effluent with concentration up to 150 mg/L. Sulfide rich effluent from the sulfate reduction process was used to precipitate HMs as metal sulfides from CBA leachate. HM removal in the range from 40 to 100% was obtained through sulfide precipitation.

Combined activated sludge with partial nitrification (AS/PN) and anammox processes for treatment of seafood processing wastewater.

An activated sludge process with partial nitrification (AS/PN) in combination with anaerobic ammonium oxidation (Anammox) process for treatment of seafood processing wastewater was developed and investigated in this research. Operating conditions of AS/PN process for coupling with Anammox process were identified as pH between 7.7–8.2 and DO as 0.5–0.9 mg L−1 to achieve over 85% COD removal as well as partial nitrification. The developed AS/PN process could produce almost equal concentration of ammonium and nitrite nitrogen in the effluent which was highly suitable for the Anammox process. Near complete removal of ammonium and nitrite was achieved during steady state Anammox process operation. Maximum nitrogen removal rate for the Anammox process was found to be 0.6 kg N m− 3 d−1. Microorganisms involved in both AS/PN and Anammox processes were identified using in situ hybridization and polymerase chain reaction techniques. The result 16S rDNA revealed 94% homology to Candidatus “Brocadia fulgida.”

Use of organic substrates as electron donors for biological sulfate reduction in gypsiferous mine soils from Nakhon Si Thammarat (Thailand)

Soils in some mining areas contain a high gypsum content, which can give adverse effects to the environment and may cause many cultivation problems, such as a low water retention capacity and low fertility. The quality of such mine soils can be improved by reducing the soils gypsum content. This study aims to develop an appropriate in situ bioremediation technology for abbreviating the gypsum content of mine soils by using sulfate reducing bacteria (SRB). The technology was applied to a mine soil from a gypsum mine in the southern part of Thailand which contains a high sulfate content (150 g kg(-1)). Cheap organic substrates with low or no cost, such as rice husk, pig farm wastewater treatment sludge and coconut husk chips were mixed (60:20:20 by volume) and supplied to the soil as electron donors for the SRB. The highest sulfate removal efficiency of 59% was achieved in the soil mixed with 40% organic mixture, corresponding to a reduction of the soil gypsum content from 25% to 7.5%. For economic gains, this treated soil can be further used for agriculture and the produced sulfide can be recovered as the fertilizer elemental sulfur.

Influence of anaerobic co-digestion of sewage and brewery sludges on biogas production and sludge quality

This research investigated operating parameters and treatment efficiency for the digestion of sewage and brewery sludge. The prime objective of this study was to enhance the quality of treated sludge for use as agriculture fertilizer and to enhance biogas production, a by-product that can be used as an energy source. Three bench-scale completely stirred tank reactor (CSTR) anaerobic digesters were operated at mesophilic condition (36 ± 0.2°C). A mixture of sewage and brewery sludge were used as substrates at ratios of 100:0, 75:25, 50:50, 25:75 and 0:100, based on wet weight basis (w/w). For each digester, the solids retention times (SRT) were 20 days. The organic loading and volatile solids loading were between 1.3–2.2 kg chemical oxygen demand (COD)/m3/day and 0.9–1.5 kg/m3/day, respectively. The digester fed with brewery sludge as co-substrate yielded higher treatment efficiency than sewage sludge alone. The removal efficiencies measured in terms of soluble chemical oxygen demand (SCOD) and total chemical oxygen demands (TCOD) ranged from 40% to 75% and 22% to 35%, respectively. Higher SCOD and TCOD removal efficiencies were obtained when higher fractions of brewery sludge was added to the substrate mixture. Removal efficiency was lowest for sewage sludge alone. Measured volatile solid (VS) reduction ranged from 15% to 20%. Adding a higher fraction of brewery sludge to the mixture increased the VS reduction percentage. The biogas production and methane yield also increased with increase in brewery sludge addition to the digester mixture. The methane content present in biogas of each digester exceeded 70% indicating the system was functioning as an anaerobic process. Likewise the ratio of brewery sewage influenced not only the treatment efficiency but also improved quality of treated sludge by lowering number of pathogen (less than 2 MPN/g of dried sludge) and maintaining a high nutrient concentration of nitrogen (N) 3.2–4.2%, phosphorus (P) 1.9–3.2% and potassium (K) 0.95–0.96%. The heavy metals, chromium (Cr) and copper (Cu) remaining in digested sludge were present at relatively high levels (Cr 1,849–4,230 and Cu 930–2,526 mg/kg dried sludge). The metals were present as organic matter-bound and sulfide-bound fractions that are not soluble and available. The digested sludge could be safely applied to soil as a plant nutrient source, without fecal coliforms or heavy metals risk. A sludge mixture ratio of 25:75 (sewage:brewery), which generated the higher nutrient concentrations (N = 4.22%, P = 3.20% and K = 0.95%), biogas production and treatment efficiency meet the Bangkok Metropolitan Administration (BMA) safety guidelines required for agricultural application. Biogas production and methane at the 25:75 ratio (sewage:brewery) yielded highest amount of VSremoved (0.65 m3/kg) and CODremoved (220 L/kg), respectively.

Effect of air flow rate and residence time on biodrying of cassava peel waste

Effect of air flow rate and residence time on biodrying of cassava peel mixed with activated sludge waste was investigated at laboratory scale. Air flow rates of 0.01 to 0.04 m3kg−1h−1 and residence times of 12 to 20 days were maintained during biodrying process. Calorific value of cassava peel increased from its initial value of 4,660 kJ kg−1 to a maximum value of 10,406 kJ kg−1 (wet weight basis) when air flow rate of 0.03 m3kg−1h−1 and residence time of 16 days were maintained during biodrying. Under this operating condition, moisture content of cassava peel reduced from its initial value of 70.40% to a final value of 24.00%. Maximum feedstock temperature of 64.25°C at the top layer and 59.00°C at the bottom layer were recorded at this condition. Air flow rate of 0.03 m3kg−1h−1 with 16-day residence time was found optimum for biodrying of mixed materials yielding an increase of 123% in calorific value.