Can We Decode the Messages of Activated Sludge Through the Respirograms?

Wastewater contains varieties of carbonaceous and nitrogenous compounds that undergo complicated biodegradation processes in wastewater treatment plants. How these different compounds are degraded by activated sludge in aerobic conditions is still a mystery. Researchers have been trying to interpret it using the oxygen uptake rate (OUR) derived from the respirograms of respective substrates. Several models have been proposed to interpret the substrate removal mechanisms using the experimental observations. Have we succeeded in understanding the messages by activated sludge correctly using these models? In this paper, the distinctive nature of the respirograms when activated sludge is fed with different substrates and the biokinetic models that have been developed to explain the substrate removal mechanisms using derived OUR profiles are reviewed. In addition, a sensitivity study was conducted on the recently evolved simultaneous storage and growth model to investigate the influence of key parameters on OUR profiles during the biodegradation process.     

Seasonal Variations in Isoprene Emission from Tropical Deciduous Tree Species

Isoprene is a dominant constituent of the global biogenic volatile organic compounds budget. It plays an important role in regulating the atmospheric trace gas composition including tropospheric ozone concentrations. In this study, monthly measurements of isoprene emission rates were carried out over a 1-year period (December 2002–November 2003) from four Indian deciduous tree species, namely Ficus relegiosa, Ficus infectoria, Pongamia pinnata, and Morus alba, using branch enclosure method. Significantly high monthly variations in isoprene emission rates were observed in all four-plant species. Also, each plant species exhibited pronounced seasonal variation in isoprene emission. Maximum isoprene emissions were observed during summer and minimum during the winter or spring months.     

Kinetics and dynamic modelling of batch anaerobic digestion of municipal solid waste in a stirred reactor

A series of batch, slurry anaerobic digestion experiments were performed where the soluble and insoluble fractions, and unwashed MSW were separately digested in a 200l stirred stainless steel vessel at a pH of 7.2 and a temperature of 38 degrees C. It was found that 7% of the total MSW COD was readily soluble, of which 80% was converted to biogas; 50% of the insoluble fraction was solubilised, of this only 80% was converted to biogas. The rate of digesting the insoluble fraction was about four times slower than the rate of digesting the soluble fraction; 48% of the total COD was converted to biogas and 40% of the total nitrogen was converted to ammonia. Soluble and insoluble fractions were broken down simultaneously. The minimum time to convert 95% of the degradable fraction to biogas was 20 days. The lag phase for the degradation of insoluble fraction of MSW can be overcome by acclimatising the culture with the soluble fraction. The rate of digestion and the methane yield was not affected by particle size (within the range of 2-50mm). A dynamic model was developed to describe batch digestion of MSW. The parameters of the model were estimated using data from the separate digestion of soluble and insoluble fractions and validated against data from the digestion of unwashed MSW. Trends in the specific aceticlastic and formate-utilising methanogenic activity were used to estimate initial methanogenic biomass concentration and bacterial death rate coefficient. The kinetics of hydrolysis of insoluble fraction could be adequately described by a Contois equation and the kinetics of acidogenesis, and aceticlastic and hydrogen utilising methanogenesis by Monod equations.     

Sodium nitrate as a methanogenesis suppressor in earthen separator microbial fuel cell treating rice mill wastewater

Environmental Science and Pollution Research - The microbial fuel cell (MFC) is one of the sustainable technologies, which alongside treating wastewater, can generate electricity. However, its...     

Role of environmental lead in the occurrence of anemia in Indian children: a systematic review and meta-analysis

Environmental Science and Pollution Research - Exposure to lead among children, as well as adults, is a major global health issue. With diverse routes of exposure (e.g., food, air, and water)...     

On the origin of forces in the wake of an elliptical cylinder at low Reynolds number

Environmental Fluid Mechanics - An analysis of forces for flow around an elliptic cylinder at low Reynolds number has been presented in this work. The finite-volume based open source code OpenFOAM...