Elvis Klaucans

The perception of sewage sludge has been shifting from waste to resource, leading to various technological proposals for its management and resource recovery. This study explores a two-step sewage sludge treatment using different pathways—physical-alkali followed by physical-acid, and physical-acid followed by physical-alkali hydrolysis—to understand the efficiency of organic matter (OM) and Kjeldahl nitrogen extraction, and protein solubilization. Hydrolysis of the sewage sludge was performed with 3 M H₂SO₄ and 2.8 M NaOH and combined with physical treatment—thermal, ultrasonication, microwave irradiation, and cavitation. The results showed that cavitation chemical hydrolysis in an alkaline environment (CCH-alkali) extracted the highest amount of OM—up to 79.0%. When further cavitation chemical hydrolysis in an acid environment (CCH alkali–acid) was performed, OM extraction reached 90.2%. Physical-alkali treatment showed better performance in resource recovery from secondary sludge (SS) in both treatment steps. The highest protein extraction rate of 23,046 mg/L in the supernatant was obtained using SS treatment with microwave chemical hydrolysis in an alkaline environment (MCH-alkali). Although physical-acid treatment resulted in reduced protein solubilization and OM extraction, it provides a higher protein hydrolysis rate. Organic nitrogen compounds were better extracted with thermal-alkali treatment, reaching 95.3% removal. The study showed that different physical treatment methods demonstrate selective resource recovery or extraction performance.

Incorporation of various alternative resources as co-digestion substrates aids to reduce the consumption of agricultural crops for biogas production. However, the efficiency and limitations of these co-substrates is still not fully understood. Use of biomass waste remaining after enzymatic hydrolysis for high value chemical fermentation, meat processing and dairy wastewater primary sludge as co-substrates in an agricultural resource anaerobic digestion plant is tackled within this study. The results showed that anionic surfactants (4/gVS for meat processing wastewater primary sludge, and from 534 to 740 mLCH₄/gVS for dairy wastewater primary sludge, when agricultural digestate is used as a substrate and sludge loading is not more than 10% from the volatile solids loaded. At the same time, only 549.7 mLCH₄/gVS was produced as 30-day BMP when 5% biomass hydrolysis waste was used. Biomass hydrolysis waste co-digestion with primary sludge from dairy and meat processing wastewaters has an antigenic effect, and separate substrate anaerobic digestion gave a better results, thus, showing that excessive combination of various waste resources can be inhibitory for biogas production and the appropriate substrate selection and combination is a technical challenge for the biogas industry.