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Coffee is one of the most significant beverages consumed worldwide, dating to times immemorial. It plays a pivotal role in several economies owing to its second position in the list of trading commodity, after petroleum. The growing demand for coffee has resulted in a great amount of coffee production and processing and subsequent release of large volumes of wastewater. This wastewater is characterized to have very high chemical oxygen demand and biological oxygen demand with potential to cause environmental pollution thus requiring smart strategies to effectively reduce their load of the wastewater before releasing them into the habitable ambiance. The existing research on coffee wastewater treatment should be critically analyzed for their sustainability and economic viability for them to be commercially used in developing countries for effluent mitigation. This literature review aims to suggest an effective way to treat the wastewater by combining various methods, coupling it with value addition like energy generation. The goal of this review is to provide a direction for future research to integrated treatment with valorization along with a focus on emerging technologies.

Pulp and paper industry is one of the high priority sectors that generates large amount of solid (sludge) and liquid (paper mill effluent) wastes. Making use of this huge quantity of paper mill sludge (PMS) in an environment friendly manner is challenging and cost involving. Similarly the present wastewater treatment strategies based on physical and chemical methods encounter certain serious setbacks including secondary pollution generation with expensive mode of abatement processes. The present study aims at a “waste treats waste” strategy for the bioremediation of paper mill effluent in fluidized bed reactor (FBR) using another waste of the same industry, PMS as immobilizing matrix for Planococcus sp. TRC1, a wastewater bacterial isolate. This study simultaneously explores this isolate for the yellowish orange pigment it produces (2.3 ± 0.2 mg/gm of dry bacterial biomass) and characterizes it as a member of the pharmacologically important carotenoid pigment family via UV-Vis spectrophotometry, TLC, FT-IR and 13C NMR. The antioxidant potential of this pigment was studied by DPPH assay (IC50 = 33 ± 0.4 μg/ml) and H2O2 assay (IC50 = 147.4 ± 2.2 μg/ml). In FBR, the PMS immobilized bacteria showed removal of phenol, lignin, colour and COD from the effluent by 96%, 74%, 81% and 85% respectively after 60hr of treatment. The experimental data on immobilization fitted well with pseudo second-order (R2 = 0.955) and Freundlich adsorption isotherm (R2 = 0.996) models. The alterations in PMS before and after bacterial immobilization, as revealed by SEM and FT-IR, depicted the success of PMS as immobilization matrix. Phytotoxicity (90% seed germination) and mutagenicity studies confirmed that the treated effluent was substantially less toxic than its raw state. This study highlights a novel utilization possibility of PMS in an eco-friendly and economic way as immobilization matrix for Planococcus sp.TRC1 for paper pulp mill effluent treatment along with production of carotenoid pigment from this potential bacterial isolate as value added product.

A potential bacterium Bacillus flexus RMWW II has been isolated from rice mill effluent, and examined for its decolorizing potential for lignin-mimicking dyes. The biodegradation of alkali lignin by the rod-shaped, Gram-positive, oxidase and catalase-positive Bacillus flexus RMWW II bacteria is due to its uptake of lignin as the sole carbon source. The lignin degradation was 100% at a lignin concentration of 50 mg L−1 but the degradation reduced to 20% at 400 mg L−1. The bacterial-mediated biodegradation of alkali lignin was suitably explained by the Edward kinetics model with a maximal specific biodegradation rate (qmax) of 0.056 h−1 and true specific biodegradation rate (q*) of 0.042 h−1. The non-toxic nature of the metabolites of alkali lignin after bacterial degradation was illustrated by phytotoxicity studies. This bacterium was utilized to treat complex rice mill wastewater, as lignin is one of the major components of the effluent. A considerable reduction of 84% of chemical oxygen demand (COD) was observed in a batch reactor in 70 h of operation. The bacterial treatment results for the actual rice mill effluent indicate that Bacillus flexus RMWW II could be a promising agent for microbial remediation of lignin-laden raw rice mill wastewater.

An economically efficient and eco-benign new approach was performed for the treatment of rice mill wastewater by Fenton-like process using rice husk ash (RHA)-based silica-supported iron catalyst. The detailed characterization of the prepared catalyst was described by SEM, XRD, and FT-IR. The maximum COD reduction of 75.5 % was achieved at response surface-optimized conditions that constitutes of catalyst dose 4.12 g/L, H2O2 concentration 4.2 g/L and pH 3.2. The non-toxic nature of the treated rice mill effluent using green catalyst was revealed by phytotoxicity. Meticulous efforts have been made for judicious utilization of one waste (RHA) against another serious waste (rice mill wastewater) abatement of the same industry. Findings clearly established that the proposed designed scheme offered a complete sustainable solution towards minimization of various wastes generated from rapidly growing rice mills.

Rice mills release huge volumes of wastewater and other by-products when processing paddy rice. The wastewater often contains toxic inorganic and organic contaminants which cause environmental damage when released. Accordingly, cost-effective techniques for removing contaminants are needed. This article reviews current processes for curbing pollution and also reusing and recycling waste products. Novel techniques exist for converting waste products into energy and value-added products.