The recent trend of turning wastewater treatment plants (WWTPs) into energy self-sufficient resource recovery facilities has led to a constant search for solutions that fit into that concept. One of them is chemically enhanced primary treatment (CEPT), which provides an opportunity to increase biogas production and to significantly reduce the amount of sludge for final disposal. Laboratory, pilot, and full-scale trials were conducted for the coagulation and sedimentation of primary sludge (PS) with iron sulphate (PIX). Energy and economic balance calculations were conducted based on the obtained results. Experimental trials indicated that CEPT contributed to an increase in biogas production by 21% and to a decrease in sludge volume for final disposal by 12% weight. Furthermore, the application of CEPT may lead to a decreased energy demand for aeration by 8%. The removal of nitrogen in an autotrophic manner in the side stream leads to a further reduction in energy consumption in WWTP (up to 20%). In consequence, the modeling results showed that it would be possible to increase the energy self-sufficiency for WWTP up to 93% if CEPT is applied or even higher (up to 96%) if, additionally, nitrogen removal in the side stream is implemented. It was concluded that CEPT would reduce the operating cost by over 650,000 EUR/year for WWTP at 1,000,000 people equivalent, with a municipal wastewater input of 105,000 m³/d.

The Heracleum sosnowskyi is a highly invasive plant species known for its rapid spread and the significant threat it poses to the ecosystem and human health, primarily due to its furanocoumarin content. In the present study, for the first time the pyrolysis process (200-600 °C) of Heracleum was conducted, demonstrating its efficacy in utilizing the material as feedstock and generating valuable solid by-products. It was found that biochar produced at temperatures of 200-300 °C is suitable for solid fuel production (HHV 20.2-24.1 MJ·kg^-1) and has strong hydrophobic properties, while pyrolysis over 400 °C promotes the improvement of fertilizing properties by increasing the content of micro and macronutrients (K=112.4 g·kg^-1 at 600 °C). The mass and energy analysis proved that in specific conditions (for dry > 300 °C; for wet > 400 °C), pyrolysis can be an effective way for Heracleum biomass conversion into valuable biochar without the need for external energy.

Reducing waste production and improving waste treatment are key objectives in the EU’s Circular Economy Action Plan. Anaerobic digestion of food waste is a promising method, but safely disposing of its by-products, which contain valuable nutrients like nitrogen, phosphorus, and organic matter, remains a challenge. These nutrients suggest potential use in agriculture to enhance sustainability, yet their effects on plant growth need thorough understanding. This study investigated the impact of liquid digestates from anaerobic digestion of food waste, combined with fish sludge (from recirculated aquaculture systems), on plant growth (Lepidium sativum and Triticum aestivum) through direct soil tests. The content of biogenic elements in the digestates did not differ and was 0.32% for N, <0.05% for P, and 0.15% for K. Two tests were conducted, both using artificial soil prepared to OECD 207 standards: the Phytotoxkit™ test (ISO 18763:2016) and a pot experiment (OECD 208). Results showed that digestates initially delayed germination and hindered early plant growth, an effect that diminished over time. This may be due to the high organic matter content of digestates, similar to standard fertilizers like manure or compost. Pre-incubating digestates in soil before application, similar to common agricultural practices with soil amendments, is suggested as a potential solution.