Improvement of biogas production and quality by addition of struvite precipitates derived from liquid anaerobic digestion effluents of palm oil wastes

Abstract

When biogas is produced, the liquid anaerobic digestion effluents (LADE) still contain pollutants. Struvite precipitation is a technique for reducing pollutants as well as recovering useful elements such as nitrogen, phosphorus, and magnesium. This study aims to precipitate struvite from LADE and use it as an additive to palm oil mill effluent (POME) feedstocks in subsequent biogas production systems (batch and continuous operational modes). Struvite precipitation was simply performed using NaOH at a pH range of 8–10 without external sources of magnesium and phosphorus. The result showed that the optimum pH for struvite precipitation was 9, giving the highest yield and purity of struvite. The addition of 5% struvite to POME feedstock improved the performance of biogas production in the continuous stirred tank reactor (CSTR) in terms of stability, high COD removal efficiencies, increased methane yields, and decreased H2S concentrations. The greatest methane yield of 509.8 mL/g-VS and the methane concentration of 65.10% were obtained in the CSTR. The significant decrease in H2S concentration in biogas can increase the energy content of biogas, save on the cost of H2S removal, reduce corrosion, and extend the operating time of gas turbines used for electricity production. The results of this study emphasize the role of integrating struvite precipitation with continuous biogas production in improving the process sustainability and economy. Struvite precipitation from LADE diminishes the polluted wastewater, decreases the long-term process problems of fouling and clogging caused by struvite, and improves the performance of the biogas production.