The Impact of Substrate–Enzyme Proportion for Efficient Hydrolysis of Hay

Enzymatic hydrolysis of waste streams originating from wastewater treatment plants

BACKGROUND

Achieving climate neutrality is a goal that calls for action in all sectors. The requirements for improving waste management and reducing carbon emissions from the energy sector present an opportunity for wastewater treatment plants (WWTPs) to introduce sustainable waste treatment practices. A common biotechnological approach for waste valorization is the production of sugars from lignocellulosic waste biomass via biological hydrolysis. WWTPs produce waste streams such as sewage sludge and screenings which have not yet been fully explored as feedstocks for sugar production yet are promising because of their carbohydrate content and the lack of lignin structures. This study aims to explore the enzymatic hydrolysis of various waste streams originating from WWTPs by using a laboratory-made and a commercial cellulolytic enzyme cocktail for the production of sugars. Additionally, the impact of lipid and protein recovery from sewage sludge prior to the hydrolysis was assessed.

RESULTS

Treatment with a laboratory-made enzyme cocktail produced by Irpex lacteus (IL) produced 31.2 mg sugar per g dry wastewater screenings. A commercial enzyme formulation released 101 mg sugar per g dry screenings, corresponding to 90% degree of saccharification. There was an increase in sugar levels for all sewage substrates during the hydrolysis with IL enzyme. Lipid and protein recovery from primary and secondary sludge prior to the hydrolysis with IL enzyme was not advantageous in terms of sugar production.

CONCLUSIONS

The laboratory-made fungal IL enzyme showed its versatility and possible application beyond the typical lignocellulosic biomass. Wastewater screenings are well suited for valorization through sugar production by enzymatic hydrolysis. Saccharification of screenings represents a viable strategy to divert this waste stream from landfill and achieve the waste treatment and renewable energy targets set by the European Union. The investigation of lipid and protein recovery from sewage sludge showed the challenges of integrating resource recovery and saccharification processes.

Microalgae Harvesting after Tertiary Wastewater Treatment with White-Rot Fungi

Tertiary wastewater treatment with microalgae incorporates environmental sustainability with future technologies and high exploitation costs. Despite the apparent ecological benefits of microalgae-assisted wastewater treatment/biomass-based resource production, technological improvements are still essential to compete with other technologies. Bio-flocculation instead of mechanical harvesting has been demonstrated as an alternative cost-effective approach. So far, mostly filamentous fungi of genus Aspergillus have been used for this purpose. Within this study, we demonstrate a novel approach of using white-rot fungi, with especially high potential of algae-Irpex lacteus complex that demonstrates efficiency with various microalgae species at a broad range of temperatures (5-20 °C) and various pH levels. Harvesting of microalgae from primary and secondary wastewater resulted in 73-93% removal efficiencies within the first 24 h and up to 95% after 48 h. The apparent reuse potential of the algae-I. lacteus pellets further complements the reduced operating costs and environmental sustainability of bio-flocculation technology.

Bioprospecting White-Rot Basidiomycete Irpex lacteus for Improved Extraction of Lignocellulose-Degrading Enzymes and Their Further Application

Lignocellulosic biomass can be used as a source for energy, fuel and valuable chemical production. From all available technologies, biological approaches have been recognized as the most environmentally friendly and sustainable ones. At the same time, high conversion costs, low efficiency and environmental issues still hinder the introduction of biological processes into industrial scale manufacturing. The aim of this study was to determine the most suitable enzyme cocktail recovery conditions from a biomass-fungal culture of the white-rot basidiomycete Irpex lacteus. Subsequent evaluation of the overall enzyme cocktail efficiency to release fermentable carbohydrates from biomass showed that prolonged fungal cultivation decreases the quality of the produced enzyme cocktail. At the same time, introduction of ultrasound pre-treatment during enzyme extraction improved the recovered enzyme cocktail efficiency in converting biomass to fermentable sugars, yielding up to 0.25 g of fermentable sugar per g dry hay biomass and up to 0.11 g per g dried straw or microalgae substrates. The results demonstrated that the production of lignocellulose-degrading enzymes from fungi is more sensitive than previously described, especially in terms of fungal growth, culture sterility and incubation conditions.