Methane Production of Algal Biomass from Facultative Stabilization Pond: Evaluation of Anaerobic Biodegradability and Codigestion with Sewage Sludge

Abstract

Anaerobic biodegradability tests of algae biomass produced on a facultative sewage stabilization pond were conducted at 33 K for up to 24 days. The addition of urea and KH2PO4 enabled the algae biomass to adjust its chemical oxygen demand∶N∶P ratio to 35∶5∶1. Comparison with the raw substrate showed that it contained sufficient amounts of N and P for bacteria metabolism. The addition of anaerobic sludge as inoculum did not affect the overall degradation efficiency but increased the initial biogas production rate, from 9.2 (without inoculum) up to 3.2 mL/days with 1% volume/volume (v/v) inoculum. The codigestion of algae biomass and anaerobic sludge was evaluated in the range of 5–5% (v/v) of algae biomass, and specific methane production of substrate combination achieved values up to 6 NmL CH4/g volatile solids, which is 1 times higher than the degradation of just raw sludge. Destruction of volatile solids also increased with the addition of algae biomass, varying from 2% degradation (with raw sludge) up to 42% when 5% (v/v) of algae biomass was added.