Currently, reservoirs, lakes, rivers etc. are being overloaded by the demand for fresh water, due to rapid industrialization and population explosion, and also the effluents from industries and domestic wastewater are continuously polluting these resources. To address this issue, several decentralized wastewater treatment system (DWTS) have been installed all over the globe to reuse and recycle wastewater/graywater for non-potable uses such as fire protection, toilet-flushing, and landscape irrigation. In this review, a comparison between different DWTS was carried out to evaluate their performance, merits and limitations. Hybrid technologies like the electrically enhanced biomass concentrator reactor and integration of physical/ biological methods with bio-electrochemical systems such as microbial fuel cells were found to be the most promising methods for near complete removal of pollutants from wastewater and also the issue of membrane fouling was reduced to a good extent.

Background. Aniline and its derivatives are widely used as intermediate chemicals in the pharmaceutical and dye industries and are present in their wastewaters. These chemicals are of concern due to their potential detrimental effects on public health and aquatic species in the environment. Objectives. Various available remedial technologies presented in the literature were investigated to determine the most suitable technology for the elimination of aniline and aniline derivatives from waste streams. Methods. The related literature was collected electronically from ScienceDirect, Google Scholar, the International Agency for Research on Cancer (IARC), ResearchGate and Wiley Online Library for systematic review. The search terms included ‘aniline’, ‘aniline degradation’, ‘advanced oxidation processes (AOPs)’, ‘aniline derivatives’ and ‘Fenton’s reagent'. Discussion. Aniline and its derivatives are a serious issue in the effluents of dye and pharmaceutical industries, but a number of efficient treatment methods using biological, physical and AOPs have been presented in the literature. Conclusions. Comparison of the available technologies showed that AOPs were the most cost effective and efficient technologies for eliminating aniline and its derivatives from wastewater. Competing interests. The authors declare no competing financial interests.

The growing contamination of various freshwater resources due to industrial effluent is a serious concern among the scientific community. Several organic compounds are essentially used as chemical intermediate in variety of industrial processes. These organic compounds are hazardous chemicals which are already considered dangerous to global public health and other forms of life due to their high toxicity, carcinogenicity. These organic contaminants are found present in the industrial effluents. Several treatment methods were applied in the literature for their elimination from wastewater to make their final disposal safe for environment. In this article, different kinds of physical, biological and advanced oxidation methods (AOPs) applied for the treatment of various important organic compounds were compared for their advantages and disadvantages. The results showed that the conventional treatment methods are not effective to treat these kinds of toxic and refractory chemical compounds. Therefore, AOPs were found to be the most promising treatment methods.

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p-Anisidine being a component of wastewater generated through dye and pharmaceutical industries is highly toxic and carcinogenic in nature. Therefore, its presence in wastewater requires prior treatment before its disposal from the point of safety of human and aquatic life. Fenton's oxidation is a type of advanced oxidation processes which is efficient, ecofriendly and reliable, and this was not studied for the removal of p-anisidine from wastewater. In this study, the effect of influent pH, hydrogen peroxide (H 2 O 2 ) concentration and ferrous ion (Fe 2+ ) concentration on the removal of p-anisidine by Fenton's reagent was carried out on a laboratory scale. All samples were examined for initial and final concentrations of p-anisidine using UV-Vis spectrophotometry, and also initial and final COD was analyzed. p-Anisidine shows maximum absorbance at 296 nm. At pH 2.5 and [H 2 O 2 ]/[Fe 2+ ] of 70:1 for the initial p-anisidine concentration of 0.5 mM and for 24 h reaction time, the maximum removal of p-anisidine was found to be 88.95% and maximum COD removal was 76.43%.