Indu Mehrotra

Treatment of wastewater from slaughterhouse by DAF-UASB system

The performance of upflow anaerobic sludge blanket (UASB) process for the treatment of slaughterhouse wastewater, with and without dissolved air flotation (DAF) as pretreatment was evaluated. Working parameters for the DAF process were evolved by bench scale studies. The biochemical methane potential (BMP) of the raw wastewater, the float and the subnatant (from DAF) was evaluated by serum bottle techniques. Results revealed higher biodegradability of the fractions as compared to the raw waste. The operation of UASB reactor at 30±1°C with pretreated waste was found to be technically feasible.

Removal of chromium from industrial effluents by adsorption on sawdust

Abstract Chromium containing wastes create toxic conditions in the environment. The treatment technology in vogue has not yielded promising results. Use. of sawdust, a waste product from wood processing industry has been explored herein. The results show significant removal by a combination of physical adsorption and solid phase reaction. The kinetics and the equilibrium capacities have been worked out. The prewashed sawdust eliminates the colour throw to a large extent.

Sludge blanket of UASB reactor : Mathematical simulation

Blanket height is an important aspect of UASB reactor design. It regulates the solid concentration reaching the gas-solid separator (GSS) and, thereby, prevents sludge washout. The maximum organic load which a reactor can assimilate depends on proper proportioning of the reactor height into the bed and blanket. A condition of force equilibrium has been considered between the rising gas bubbles and the adjacent water mass. The negative pressure behind the bubble attracts the water mass and leads to the formation of a wake. Using diffusion concepts, solid particles moving along the wake due to concentration gradient have been equated to those settling down under the influence of gravity at steady state and solid concentration along the blanket height is ascertained. Computed values have been found to compare well with the scanty experimental observations available from the literature. Using this model, it is possible to size the reactor.

Impact of riverbank filtration on treatment of polluted river water.

The impact of riverbank filtration (RBF) on the treatment of water from the River Yamuna at Mathura, which has disagreeable visual properties, has been investigated. The dissolved organic carbon (DOC) and colour of the river water were 4.0-6.8mg/L and 40-65 colour units (CU), respectively. Pre-chlorination is in practice to improve raw water quality. Chlorine doses as high as 60mg/L ahead of the water treatment units reduced colour by about 78%. Removal of DOC and UV-absorbance was less than 18%. In comparison to direct pumping of the river water, collection of water through RBF resulted in the reduction of DOC, colour, UV-absorbance and fecal coliforms by around 50%. However, riverbank filtrate did not conform to the drinking water quality standards. Therefore, riverbank-filtered water along with the Yamuna water were ozonated for different durations. To reduce DOC to the desired level, the dose of ozone required for the riverbank filtrate was found to be considerably less than the ozone required for the river water. RBF as compared to direct pumping of Yamuna water appears to be effective in improving the quality of the raw water.

Treatment of phenolic wastewater in UASB reactor: Effect of nitrogen and phosphorous

Phenolic wastewater representing an industrial wastewater was supplemented with varying amount of nitrogen (N) and phosphorous (P) and treated in upflow anaerobic sludge blanket reactor (UASBR). The variation of COD:N:P from 300:10:1 to 300:1:0.1, did not influence the conversion of phenol COD to methane COD. The concentration of N and P in the influent was reduced from 25.5mgl(-1) to 2.5mgl(-1) and 2.5 to 0.25mgl(-1), respectively. However, on further reducing the nutrients in the feed from 300:1:0.1 to 300:0:0 the (i) CH(4)-COD decreased from 90% to 40%, and (ii) cell yield reduced to 25-50%. The average cell yield was 3.5%. Percent N and P in cells varied from 10% to 14% and 0.6% to 2.4%, respectively. The activity of the sludge assessed as specific methanogenic activity (SMA) was found in the range from 0.15 to 0.66g CH4-CODg(-1) VSSd(-1). The optimum COD:N:P for phenolic wastewater has been estimated to be 300:1:0.1.

Experimental and modeling investigations of a hybrid upflow anaerobic sludge-filter bed (UASFB) reactor

A 9.8-L hybrid UASFB reactor, in which the lower half was occupied by a sludge blanket and the upper half by small floating polyethylene media, was evaluated using wine distillery vinasse as substrate. The reactor was operated for a total period of 232 days at 33 + 1 degrees C. Continuous feeding of the reactor was started with an initial OLR of 2.9 g COD/L.d and then it was increased step wise to 19.5 g COD/L.d by increasing the feed COD, while maintaining a constant HRT (1.05 d). The reactor was equipped with a continuous internal recirculation system from top to the bottom at the rate of 9 L/h (upflow velocity = 0.83 m/h) upto day 159 and then it was reduced to about half on day 160 onwards. It was observed that the reduced recirculation rate did not affect the performance of the reactor with an average COD(t) and COD(s) removal efficiencies of 82 and 88%, respectively. A maximum gas production rate of 6.7 L CH(4)/L(reactor).d was achieved for the highest OLR applied. The specific activity analysis depicts that the activity of the attached biomass was more than 2 times higher than that of the granular sludge. The efficiency of liquid mixing was good through out this study. The packing medium had a dual role in the retention of the biomass inside the reactor: i.e. entrapment of biomass within the support and filtration of the granular biomass, preventing it from going out of the reactor. ADM1_10 model simulated well the dynamic evolutions of the main variables in the liquid as well as in the gas phases.

Simultaneous extraction scheme: A method to characterise metal forms in sewage sludge

Abstract To study the speciation of metals in sludges an attempt has been made to develop a simultaneous extraction technique by modifying the sequential extraction technique of Stover et al. In our simultaneous extraction procedure, different metal forms are additively extracted by an appropriate combination of reagents. Copper, zinc and cadmium in six samples of digested sludge (three liquid and three air dried) were fractionated by simultaneous as well as sequential extraction procedures. Similar metal profiles were obtained from these two techniques. Therefore, the method proposed herein can be suitably used as a complementary procedure to obtain a metal distribution pattern.

Performance of UASB based sewage treatment plant in India: polishing by diffusers an alternative.

In India, recently, upflow anaerobic sludge blanket (UASB) based sewage treatment plants (STPs) have come up in a big way. Sequence adopted: screens- grit chambers- UASB reactors followed by one-day detention ponds (DP). Performance of DPs located at five STPs (27-70 ML/d) was evaluated over a period of one year from July 2004 to July 2005. The installation of these non-algal ponds reduced land requirement, but from treatment point of view it at best offered only removal of solids washed out of the UASB reactor. Total coliform count in the effluent from ponds ranging from 10(6) to 10(9) MPN/100 mL is more than the maximum permissible limit of 10,000 MPN/100 mL. A need has, therefore, been felt to evaluate the possibility of aerating the effluent from UASBR. During aeration, ORP and DO increase, whereas COD and BOD decrease. In a continuous aeration ~50% reduction in COD and nearly 50% increase in DO saturation (DO/DOs) can be achieved by increasing ORP from -100 to 122 mV. Regression equation established between ORP and COD/CODi & DO/DOs may find wide application.

Application of risk-based assessment and management to riverbank filtration sites in India

This is the first reported study of a riverbank filtration (RBF) scheme to be assessed following the Australian Guidelines for Managed Aquifer Recharge. A comprehensive staged approach to assess the risks from 12 hazards to human health and the environment has been undertaken. Highest risks from untreated ground and Ganga River water were identified with pathogens, turbidity, iron, manganese, total dissolved solids and total hardness. Recovered water meets the guideline values for inorganic chemicals and salinity but exceeds limits for thermotolerant coliforms frequently. A quantitative microbial risk assessment undertaken on the water recovered from the aquifer indicated that the residual risks of 0.00165 disability-adjusted life years (DALYs) posed by the reference bacteria Escherichia coli O157:H7 were below the national diarrhoeal incidence of 0.027 DALYs and meet the health target in this study of 0.005 DALYs per person per year, which corresponds to the World Health Organization (WHO) regional diarrhoeal incidence in South-East Asia. Monsoon season was a major contributor to the calculated burden of disease and final DALYs were strongly dependent on RBF and disinfection pathogen removal capabilities. Finally, a water safety plan was developed with potential risk management procedures to minimize residual risks related to pathogens.

Anaerobic degradation of benzoate: batch studies.

Response of benzoate along with phenol to different anaerobic inocula has been investigated in batch reactors. In Phase I, the anaerobic biodegradability of benzoate and phenol were evaluated using (a) washed acclimatized granular sludge (WAGS) collected from a passive phenol fed bench-scale up-flow anaerobic sludge blanket reactor (UASBR) and (b) unacclimatized flocculent sludge (UFS) from a UASB based sewage treatment plant (STP). The effect of varying concentrations of benzoate has been investigated in Phase II using acclimatized granular sludge (AGS) from a bench-scale UASBR. Extent of degradation of benzoate was more than the phenol. Increasing benzoate COD from 2500 to 11,700mg/L, resulted in decrease in (i) rate constant, k from 0.79 to 0.11/d and (ii) ultimate biochemical methane potential (microb, g CH4-COD formed/g benzoate COD) from 84% to 60%. Temporal trend conforming to logistic S-curve indicated stressed conditions at higher benzoate concentration. Benzoate degradation was found to be sensitive to nature as well as quantity i.e. food to microorganism (F/M) of inocula used.