Purpose This study investigated the chemical characteristics and anaerobic digestion of Chlorella sp. microalgae cultivated on various anaerobic digestion effluents (ADEs) as a nutrient medium. Chlorella sp. was grown in anaerobically digested effluent of dairy wastewater (DW), municipal wastewater sludge (WS), maize silage and swine slurry, and cattle manure (CM). Methods To evaluate the anaerobic biodegradability of harvested biomass, 20-days batch anaerobic digestion experiments were used. Results It was found that a nutrient medium directly affected nitrogen concentration in the cultivated biomass, as well as the C/N ratio value which ranged 7.2–12.9. Higher C/N ratio of the Chlorella sp. cultivated on DW and WS significantly enhanced the methane production, which was 241 ± 5.5 mL CH₄/g VS and 267 ± 10.9 mL CH₄/g VS, respectively. The highest biogas production rate of 61.28 ± 2.7 mL/g VS·d and methane concentration in biogas of 69.7 ± 4.1 % were obtained during the digestion of Chlorella sp. biomass cultivated on WS. Conclusions These results proved the applicability of ADEs as a nutrient medium for Chlorella sp. cultivation and the impact of a nutrient source on C/N ratio in harvested biomass, which subsequently affected the biogas/methane yield.

In this paper, we discuss the effect sewage sludge (SS) application has on the contamination of polycyclic aromatic hydrocarbons in fertilized soils and groundwater. Morver, the contents of these compounds in plant biomass was analyzed. For six months, composted sewage sludge was introduced into sandy soil. The research was conducted under lysimetric experiment conditions with the possibility of collecting soil leachate in natural conditions. The following doses of sewage sludge were used: 0, 10, 20, 30, and 40 t/ha calculated per experimental object containing 10 kg of sandy soil. The examinations were carried out within a three-year time frame. Dactylis glomerata grass was grown on the fertilized soils. Every year, the content of polycyclic aromatic hydrocarbons (PAHs) was collected from fertilized objects and analyzed in soil leachate, which can contaminate surface water. The following six polycylic aromatic hydrocarbons defined by Polish standards were determined: benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenz(a,h)anthracene, and benzo(g,h,i)perylene, indeno(1,2,3-cd)pyrene. Further, the content of PAHs in soils and the bioaccumulation of these compounds in cultivated plants were evaluated after each year. The results of the study showed that the increase in the dose of sewage sludge used for soil fertilization led to the rise in the amount of polycyclic aromatic hydrocarbons analyzed in the soil. The compounds migrated to cultivated plants. This phenomenon was observed especially in the first year following soil fertilization with sewage sludge. Excessive accumulation of PAHs (especially benzo(a)pyrene) was observed in plant biomass in the first year of a lysimetric experiment after sewage sludge fertilization with doses greater than 10 t/ha. The increase in bioaccumulation of this compound in plant biomass compared to control objects was 138%, 288%, and 505% after application of 20, 30, and 40 t/ha, respectively. Fertilization with sewage sludge did not cause contamination with PAHs in water leachates from the soils.