Preparation of polyvinyl alcohol-calcium sustained-release agent employed to degrade long-chain fatty acids and improve the performance of anaerobic digestion of food waste

Abstract

Polyvinyl alcohol (PVA) is a biodegradable material that can be degraded under natural conditions. In this study, a sustained-release agent (SRA) was prepared from calcium compounds and PVA (PVA-Ca) to effectively degrade long-chain fatty acids in food waste (FW) and improve the performance of anaerobic digestion (AD). The most appropriate materials and conditions for synthesizing Ca-SRA were chosen according to the characteristics of the sample and changes in the electrical conductivity of a solution of the SRA. The calcium release kinetics were analyzed by curve fitting. Moreover, analytical methods were used to analyze the formation mechanism of PVA-Ca. Finally, the effect of PVA-Ca on the performance of AD was investigated. The results showed that the most suitable materials for preparing the Ca-SRA were Ca(OH)2 powder and PVA1799. The most suitable synthesis conditions were freezing for 24 h at −20 °C and thawing for 24 h with one freeze–thaw cycle. PVA-Ca achieved rapid release during the first 48 h, which corresponded to first-order kinetics (k = 0.0354 h−1). The release of Ca2+ corresponded to changes in pH and the concentration of volatile fatty acids during hydrolysis and acidification of FW. After PVA-Ca was added, the duration of the system lag phase was significantly shortened to 10 days, the methane yield per unit load was increased from 238.2 to 489.3 mL g−1 volatile solids(VS), and the kinetic constant of AD of FW was 0.083 day−1. Adding PVA-Ca could increase the methane yield by 98.82%. Moreover, the value of T90 was reduced to a maximum of about 16 days. PVA-Ca was successfully employed in the AD of FW for the first time.