Appraisal of water quality and ecological sensitivity with reference to riverfront development along the River Gomti, India

The conflict between the vitality of natural ecosystem versus artificially developed systems has existed since decades. The ecological sensitivity and socio-economic aspects associated with riverfront development along rivers have attracted the attention of environmentalists and ecologists across the globe. The present study evaluates the impacts of channelization and riverfront development on the water quality of river Gomti through Water Pollution Index (WPI) and other statistical tools. Of the total studied sites, 75% were found to be in the ‘highly polluted’ category even after the development of riverfront. An approximate increase of 274.5% and 171.76% was witnessed in the WPI values at the midstream sites of Kudiaghat and Daliganj, respectively. This increase in the WPI values clearly stated the deteriorated water quality of river Gomti after the channelization. The major issue of domestic sewage discharge with partial or no treatment into the river seems to be unresolved even after a considerable period of riverfront development. This study can provide a reference database toward development of such projects across the globe.

Sanitary sewage

The treatment and disposal of domestic sewage is one of Brazil's main challenges. Sewage composition varies with the habits of the population and the frequency with which new contaminants are released into the environment. This study is a bibliographical review of the main aspects related to the characterization and composition of sanitary sewage, types of sewage treatment systems and pertinent legislation; and toxicity of domestic effluents. The review was based on publications available on Science Direct, Google Scholar and Scielo, as well as on printed publications, relevant legislation, and normative instructions. The research period adopted for the selection of publications was from 2005 to 2021. We found out that, in addition to the levels of organic matter from domestic sewage, residues from products used in daily life, such as pharmaceuticals and cleaning products, can be found in effluents in concentrations harmful to the environment. Often, the types of treatment used in municipal sewage treatment plants do not efficiently remove these contaminants. Thus, even if sewage is treated to meet the limits required for the physical-chemical and biological parameters established by law, domestic effluent can present a high potential for toxicity to various aquatic species such as microcrustaceans, mollusks and fish. Thus, ecotoxicological analyses represent a remarkable mechanism for indicating the efficiency of removal of emerging contaminants present in treated sanitary effluent, in addition to indicating the deleterious effects caused by these residues to the environment and ecosystems associated with the receiving water body.

Modern approaches to treatment and recovery of secondary sludge of domestic sewage

For today, pollution of the environment, in particular of surface waters, has led to an environmental crisis in many countries of the world. One of the reasons for this is the use of outdated approaches to the treatment and recovery of sewage sludge. The article presents the results of the study of literary sources in order to analyze the proposals for the treatment of secondary sludge of domestic sewage in different countries. To neutralize sewage sludge, scientists consider the possibility of obtaining fertilizes under conditions of biosulfidogenesis during the dissimilation recovery of poorly soluble sulfates or the use of enhanced oxidation technology. A new concept of domestic sewage treatment has also been proposed, which can solve the issue of sewage sludge control at the place of its forming. The main areas of sustainable sludge control are its use in agriculture as fertilizer and for the reclamation of devastated or degraded lands, as well as energy recovery by burning and alternative thermal methods such as pyrolysis, quasi-pyrolysis and gasification. It was established that the applicability of this or that technology of sewage sludge recovery depends on many local factors, in particular: productivity of sewage station; composition and methods of sewage treatment and its sediments; efficiency of sewage treatment plants; climatic zone of the sewage system location; availability of energy and material resources, etc. Today, it is relevant to monitor the qualitative composition of sewage sludge, as well as soils and natural waters regarding pollutants that can be detected in the sewage of the corresponding settlement, in order to make operational decisions to control environmental risks, as well as conduct scientific research to improve recycling and recovery technologies for sewage sludge of various composition in agricultural systems, which will help to protect the environment against pollution and rational use of land.

Employing Artificial Neural Networks to Predict the Performance of Domestic Sewage Treatment Terminals in the Rural Region

Domestic sewage in rural regions is mainly treated by small-scale treatment terminals in China. The large quantities and high dispersion of these terminals render the chemical measurement of effluent to be a time and energy intensive work and further hinder the efficient surveillance of terminals’ performance. After a thorough investigation of 136 operating terminals, this study successfully employs two artificial neural network (ANN) models to predict effluent total nitrogen (TN) and COD (R2 both higher than 0.8) by setting some easily detectable parameters, e.g., pH and conductivity, as inputs. To prevent ANN models getting stuck on local optima and enhance the model performance, genetic algorithm (GA) and particle swarm optimization (PSO) are introduced into ANN, respectively. By comparison, ANN-PSO excels in modelling both TN and COD. The root mean square error (RMSE) and R2 of ANN-PSO in modelling TN are 9.14 and 0.90, respectively, in the training stage, and 11.54 and 0.90, respectively, in the validation stage. The RMSE and R2 of ANN-PSO in modelling COD are 22.10 and 0.90, respectively, in the training stage, and 26.57 and 0.85, respectively, in the validation stage. This is the first study to provide performance prediction models that are available for different terminals. Two established ANN-PSO models show great practical significance in monitoring huge amounts of terminals despite the slight sacrifice of models’ accuracy caused by the great heterogeneity of different terminals.

A Comparative Study of the Growth and Nutrient Removal Effects of Five Green Microalgae in Simulated Domestic Sewage

Microalgae have shown great potential in wastewater treatment. This study evaluates the growth and nutrient removal characteristics of five different microalgae strains, namely Chlorella vulgaris, Tetradesmus obliquus, Parachlorella kessleri, Hydrodictyon sp., and Scenedesmus quadricauda, in simulated domestic wastewater. The five microalgae could adapt to wastewater, but the growth potential and nitrogen removal capacity were species dependent. The nutrient removal effect of the microalgae used in this experiment was about 50% in the first two days. Parachlorella kessleri, selected from the five strains of green algae, shows good potential in removing nutrients from simulated domestic wastewater. For the simulated domestic sewage treated with Parachlorella kessleri, the chemical oxygen demand was almost completely reduced, and ammonium-N (NH4-N) and total nitrogen (TN) removal exceeded 70% at the end of the 10-day treatment. Total phosphorus (TP) removal was slightly worse, more than 65%. Parachlorella kessleri showed the best growth in sewage with the highest biomass reaching 366.67 mg L−1 and the highest specific growth rate reaching 0.538 d−1. This study can provide a reference for selecting suitable microalgae species to treat actual domestic sewage.