Debabrata Mazumder

Applications of the deep-shaft activated sludge process in wastewater treatment

The deep-shaft activated sludge process is a unique modification of the activated sludge system. The main objective of this system is to increase the amount of dissolved oxygen available for biological activity. This can be achieved by increasing the rate of oxygen transfer from the gas phase to the liquid phase. The deep-shaft configuration increases the partial pressure of oxygen, thereby causing a high saturation concentration in the reactor. In the deep-shaft process, owing to high oxygen availability, a higher organic loading can be accommodated with a comparatively low air supply. This reduces the energy and area requirements and lowers the overall cost of treatment. This technology has been successfully applied for the high-rate treatment of strongly polluted wastewater, as well as for the treatment of wastewater containing toxic or slowly biodegradable pollutants. This paper presents different applications of the deep-shaft activated sludge process, along with their relative performances.

Hybrid reactor system for wastewater treatment – application and approach of modelling

Wastewater treatment by the hybrid reactor system has become wide-spread as it provides advantages of both the suspended and attached growth phase at the same time. It may be used to treat some rate-limiting substrate, priority pollutants, volatile organic compounds etc. as well as for nitrification. This versatile nature of hybrid reactor demands for a detailed investigation on the mechanism, mode of operation, different applications and major configurations available. The present article is devoted to explore these issues with respect to previous background and successive development in this area. Apart from the laboratory and pilot-scale study, some industrial applications have been overviewed to understand the performance of hybrid reactor in the concerned field. The approach of modelling for the hybrid reactor system is also demonstrated with the hypothetical data set. A comprehensive details about major hybrid processes is presented along with their schematic diagrams. The review on hybrid process revealed that it would be economic for upgradation of existing activated sludge system, ensuring carbonaceous oxidation and nitrification in a single reactor and treatment of slowly bio-degradable substances also.

Simultaneous COD and ammonium nitrogen removal from a high-strength wastewater in a shaft-type aerobic hybrid bioreactor.

A hybrid model of activated sludge reactor has been developed in laboratory scale to explore the feasibility of carbon oxidation along with nitrogen removal through nitrification and denitification in the same reactor. The reactor was operated initially under suspended growth only and then hybrid system containing 20 g/L of tyre tube beads. The reactor was operated continuously with the high strength composite synthetic wastewater containing COD and NH4 + -N in the range of (1000 - 3500) mg/L and (500 - 1750) mg/L respectively that follows COD : NH4 + -N equals to 2 : 1. About 80% removal of COD was achieved at a HRT of 8 hrs. even under purely suspended growth condition. At least 12 hrs. HRT was needed to achieve more than 90% NH4 + -N removal for an influent NH4 + -N of 1000 mg/L or more. Nitrite and nitrate formation was promoted with the addition of attached biomass by means of bio-carriers. The maximum extent of nitrite and nitrate formation was about 43.9% and 35.3% of influent NH4 + -N respectively.

Treatment of distillery anaerobic effluent in a hybrid biological reactor

The treatability of anaerobic effluent from a molasses-based distillery was studied in a shaft-type hybrid bioreactor under purely suspended growth and hybrid system containing 5 mm tyre-tube beads. The Ks, k, Y and k found as 111.29 mg/l, 0.026/h, 0.4607 and 0.0040/h respectively. The maximum COD removal was 51.7% at a loading rate of 5.250 kg d−1 m−3. The overall removal rate was 0.0431, 0.0452, 0.0484 and 0.053/h under 0, 10, 20 and 30 g/l of beads respectively. When attached biomass increased, the cell synthesis part of oxygen utilisation coefficient gradually decreased and that for endogenous respiration increased.

Scope of improvement of treatment capacity of activated sludge process by hybrid modification

Activated sludge process is widely used for wastewater treatment throughout the world with various needful modifications. The hybrid modification of conventional activated sludge process utilizes a...

A new approach for development of kinetics of wastewater treatment in aerobic biofilm reactor

AbstractBiofilm process is widely used for the treatment of a variety of wastewater especially containing slowly biodegradable substances. It provides resistance against toxic environment and is capable of retaining biomass under continuous operation. Development of kinetics is very much pertinent for rational design of a biofilm process for the treatment of wastewater with or without inhibitory substances. A simple approach for development of such kinetics for an aerobic biofilm reactor has been presented using a novel biofilm model. The said biofilm model is formulated from the correlations between substrate concentrations in the influent/effluent and at biofilm liquid interface along with substrate flux and biofilm thickness complying Monod’s growth kinetics. The methodology for determining the kinetic coefficients for substrate removal and biomass growth has been demonstrated stepwise along with graphical representations. Kinetic coefficients like K, k, Y, bt, bs, and bd are determined either from the intercepts of X- and Y-axis or from the slope of the graphical plots.

Development of a simplified biofilm model

AbstractA simplified approach for analyzing the biofilm process in deriving an easy model has been presented. This simplified biofilm model formulated correlations between substrate concentration in the influent/effluent and at biofilm–liquid interface along with substrate flux and biofilm thickness. The model essentially considered the external mass transport according to Fick’s Law, steady state substrate as well as biomass balance for attached growth microorganisms. In substrate utilization, Monod growth kinetics has been followed incorporating relevant boundary conditions at the liquid–biofilm interface and at the attachment surface. The numerical solution of equations was accomplished using Runge–Kutta method and accordingly an integrated computer program was developed. The model has been successfully applied in a distinct set of trials with varying range of representative input variables. The model performance was compared with available existing methods and it was found an easy, accurate method that can be used for process design of biofilm reactor.

Performance evaluation of a shaft-type hybrid bioreactor for the removal of carbonaceous organic matter

In comparison to an activated sludge process, the organics removal performance of a lab-scale hybrid bioreactor of volume 14.5 L was studied using waste automobile tyre-tube beads as bio-carrier. Batch study was performed using synthetic wastewater with soluble chemical oxygen demand (COD) ranging between 1000–3500 mg/L for a period up to 9 h under purely suspended growth as well as hybrid condition with bio-carrier concentrations in the range of 10–30 g/L of reactor volume. Hybrid condition showed significant improvement in biomass settleability and organics removal with average COD removal efficiency of 89.6% as compared to 70.6% under purely suspended growth condition.

Performance evaluation of an aerobic biofilter with high organics containing synthetic wastewater

The organics removal performance of a lab-scale aerobic biofilter of volume 0.6 L was studied using synthetic wastewater and waste automobile tyre-tube beads as media. The column study was performed under Chemical Oxygen Demand (COD) in the range of 500-1500 mg/L at an empty bed contact time (EBCT) of 2 h. The treatability constant at 27 o C was found to be 41.963. A maximum COD removal efficiency of about 90% was attained at a COD loading rate of about 6 kg/m 3 /day. The biofilter handled a COD loading rate of about 17.9 kg/m 3 /day showing a COD removal efficiency of about 76%.

Development of a simplified model for the fixed biofilm reactor.

A simplified fixed biofilm model was developed to formulate the relationship between the substrate concentrations at both the entry and exit, at the biofilm-liquid interface and at the biofilm attached surface along with average substrate flux in the biofilm, substrate flux at the biofilm-liquid interface and effective biofilm thickness. The model considered the substrate mass transport external to the biofilm and into the biofilm as per Ficks law and the steady state substrate as well as biomass balance for attached growth microorganisms. Monods growth kinetics has been adopted in substrate utilization, incorporating relevant boundary conditions. The numerical solution of model equations was accomplished for calculating average flux and exit substrate concentration and thereafter the Runge-Kutta method was employed for determining effective biofilm thickness. Consequently, two computer programs were developed for the purpose of rapid solution. The model was satisfactorily applied to data available from the literature for checking its accuracy and was validated with the experimental results. The model was found to be an easy, accurate and fast method that can be used for process design of a fixed biofilm reactor.