Search

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.

Rice is one of the imperative staple foods, particularly in the developing countries. The exponential boom in human population has resulted in the continuous expansion in the rice industry in order to meet the food demands. The various stages of paddy processing release huge quantity of solid wastes, mainly rice husk, rice husk ash and liquid wastes in the form of rice industry wastewater. The discharge of the rice industry wastewater imparts a substantial threat to the aquatic bodies and the nearby surrounding and, thus, consequently demands eco-benign treatment plan. As a result, different strategies are needed to enhance the effluent quality and minimize the operational cost of the treatment process. Therefore, efficient technological approach targeting the minimization of pollution as well as assuring the economic prosperity should be implemented. In this review article, several aspects related to the rice industry discussing the significant challenges involved in the generation of both solid and liquid wastes, mitigation experiments and future prospects have been meticulously elaborated. Furthermore, the article also focuses on the various processes utilized for reducing the pollution load and promoting the practice of reuse and recycle of waste rather than the discharge action for the sake of sustainability and the emergence of novel techniques for the generation of energy and value-added products.

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.

Kraft lignin (KL) is the chief contaminant which is responsible for dark coloration, toxicity and high chemical oxygen demand (COD) of paper pulp mill effluent. The present study investigated the diverse potentials of Planococcus sp. TRC1 in the biodegradation of KL. Preliminary evaluation indicated that the strain was able to grow on broad spectrum of lignin-derived compounds, decolorize lignin-mimicking dyes and catabolize substrates of ligninolytic enzymes. Response surface methodology (RSM) was executed to perform the optimization of different process parameters. The results displayed that Planococcus sp. TRC1 could completely utilize 100 mg L−1 of KL and 78% of 200 mg L−1 of KL as sole source of carbon with concurrent reduction in COD and color. The biokinetic details of KL biodegradation showed that the values of $$\mu^{*}$$ , µ max, $$q^{*}$$ and q max were 0.018 h−1, 0.01 h−1, 0.023 g g−1 h−1 and 0.05 g g−1 h−1, respectively. UV–visible spectrophotometry, SEM and FTIR indicated the significant alterations in the surface morphology, functional groups and chromophores during the course of biodegradation. XRD revealed the emergence of peak signifying the formation of low molecular weight intermediates after bacterial treatment. Considering the environmental impact, bacterial-treated KL illustrated less phytotoxicity using Vigna radiata seed bioassay. These results suggested that Planococcus sp. TRC1 could be a promising strain for the degradation of KL in an ecofriendly way.

Lignocellulose biomass predominantly constitutes the main feedstock for pulp and paper industry. Though some products of pulp and paper industry require the presence of lignin content, for most of the useful products formation lies in the efficient and selective removal of lignin component to make use of the intact cellulose fraction during the pretreatment of pulp. Lignin is a recalcitrant heteropolymer comprised of several complex stable bonds and linkages. The chemicals or intense energy processes used for delignification process release the hazardous chemicals compounds in the wastewater which cause toxicity and environmental pollution. The implementation of bacterial species has elucidated an effective approach in the generation of value-added products while degrading lignin from pulp biomass as well as detoxification of effluent. The direct use of bacterial cells in lignocellulose biomass and wastewater streams is promising as it outperforms the practical and technical constraints largely confronted by fungal and enzymatic means. The present review paper thus unleashed the potential of ligninolytic bacteria towards delignification of pulp biomass and treatment of effluent together with bioconversion of biomass and lignin into value-added products. Graphical abstract Schematic illustration of potential possible contribution of ligninolytic bacteria towards pulp and paper industry.

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.