Enzyme Recovery from Biological Wastewater Treatment

Ziyi Liu,Stephen R Smith

doi:10.1007/s12649-020-01251-7

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

Highlights

Enzymes are biocatalysts produced by cells and are involved in almost all metabolic processes performed by living organisms
An advantage of enzyme catalysed processes is that they demonstrate high reaction and substrate specificity, and, there are few if any side-reactions and little or no waste by-products
The optimum recovery method for a specific enzyme type can be designed depending on its location within the sludge floc and whether it is extracellular within the LB-extracellular polymeric substances (EPS) or TB-EPS, or attached to the cell surface, or intracellular, as this determines the ease of separation from microbial cells

Summary

Graphic Abstract

Keywords Activated sludge · Enzymes · EPS · Cell disruption · Hydrolytic · Resource recovery · Sonication · Wastewater treatment. This review provides a critical assessment of the stateof-the-art of scientific developments and techniques for recovering high-value enzyme products from waste activated sludge (AS) produced by biological wastewater treatment processes. A systematic and critical summary of enzyme recovery systems is presented, which demonstrates the potential for full-scale industrial application. Critical areas of understanding include: enzyme distribution in sludge, the mechanisms of enzyme extraction and product formulation, and the technical feasibility of upscaling the enzyme recovery process in practice. The potential benefits and applications of recovered enzyme products are discussed, and recommendations for future research are provided

Introduction

Method

Conclusions and Future Outlook

BCC Research

Findings

19. Eurostat