Enzyme Recovery from Biological Wastewater Treatment

Abstract

Enzymes are high value industrial bio-catalysts with extensive applications in a wide range of manufacturing and processing sectors, including the agricultural, food and household care industries. The catalytic efficiency of enzymes can be several orders higher compared to inorganic chemical catalysts under mild conditions. However, the nutrient medium necessary for biomass culture represents a significant cost to industrial enzyme production. Activated sludge (AS) is a waste product of biological wastewater treatment and consists of microbial biomass that degrades organic matter by producing substantial quantities of hydrolytic enzymes. Therefore, enzyme recovery from AS offers an alternative, potentially viable approach to industrial enzyme production. Enzyme extraction from disrupted AS flocs is technically feasible and has been demonstrated at experimental-scale. A critical review of disruption techniques identified sonication as potentially the most effective and suitable method for enzyme extraction, which can be scaled up and is a familiar technology to the water industry. The yields of different enzymes are influenced by wastewater treatment conditions, and particularly the composition, and can also be controlled by feeding sludge with specific target substrates. Nevertheless, hydrolytic enzymes can be effectively extracted directly from waste AS without specific modifications to standard wastewater treatment processes. Purification, concentration and stabilisation/immobilisation techniques can also greatly expand the industrial application and increase the economic value and marketability of enzyme products extracted from AS. Concentrated and purified AS enzymes could readily substitute inorganic and/or commercial bioenzyme catalysts in many industrial applications including, for example, leather processing, and in detergent and animal feed formulation. Enzyme extraction from AS therefore offers significant economic benefits to the Water Industry by recovering valuable resources from wastewater. They can also optimise important waste treatment processes, such as the anaerobic digestion (AD) of sewage sludge, increasing biogas and renewable energy production. The enzyme-extracted sludge exhibits improved treatment properties, such as increased settleability, dewaterability, and anaerobic digestibility for biogas production, assisting sludge management by wastewater treatment plants (WWTPs) and enabling the further utilisation of the residual sludge. Graphic Abstract

Enhanced Wastewater Treatment by Immobilized Enzymes

“…Due to catalytic conversion of hazardous molecules, it is possible to obtain products, characterized by lower toxicity, compared to substrates. Besides achievement of high removal rate, enzymatic conversion leads to production of less toxic products, which might be easily separated from post-reaction mixture [32]. However, free enzymes suffer due to their low stability and extremely limited reusability.…”

Challenges and Recent Advances in Enzyme-Mediated Wastewater Remediation—A Review

“…This could be because industrial enzymes are considered a significant alternative to conventional chemical catalysts due to the attractive advantages they offer, including their accessibility from renewable resources, substrate and product stereochemistry selectivity, and fewer subsidiary reactions, and thus fewer waste byproducts. In addition, industrial enzymes show better catalytic efficiency than normally applied catalysts under mild pH and temperature conditions [147,149]. To date, there is limited economic analysis of enzyme-based biocatalysts, and thus, the cost-effectiveness of enzymes continues to be an intensively debated topic in industrial applications, particularly due to the harsh conditions that normally occur, namely, high pressures and temperatures, low and high pH, and oxidative environments.…”

Wastewater Valorization: Practice around the World at Pilot- and Full-Scale

“…In this context, this review paper aims to provide a global and comprehensive view of the status of resource recovery at pilot-and full-scale WRRFs worldwide, with special focus on water recovery as the main valuable compound and also highlighting the importance of recovering other resources, namely biomass (as microalgae and single cell protein), energy (as biogas), nutrients (as fertilizers), or more novel biomaterials such as volatile fatty acids (VFA), polyhydroxyalkanoates (PHA), and exopolymeric substances (EPS) (Figure 1). Apart from the resources recovered from wastewater that will be described in this review paper, there are reports on the literature on the recovery of other types of resources with industrial interest, namely metals, sludge-based adsorbents, materials for the building sector, and proteins and enzymes [6][7][8][9] that will not be included in this review paper. The treatment of wastewater by traditional (activated sludge) or novel technologies (such as biofilm systems such as granular sludge) based on the use of biological processes is often preferred/adopted because of their cheaper operational expenditures (i.e., no chemicals required) and their lower environmental impact in comparison to physicochemical processes.…”