Enhancement of Biogas Production by Using a Two-Stage Process for the Anaerobic Digestion of Cheese Whey

Abstract

Cheese making companies have a specific product that is seasonally produced and, like most other agro-industries, generate wastewaters characterized by a high organic loading. Cheese whey is the most important waste stream produced having a high organic content (up to 70 g COD/L), which is highly biodegradable, and low alkalinity (50 meq/L). Cheese production industries worldwide generate more than 145 million tones of liquid whey per year. Because of these characteristics, cheese whey may cause serious environmental problems on the local municipal sewage treatment systems or water receptors if disposed untreated. Anaerobic digestion is a particularly attractive treatment solution for high strength wastewaters due to the operational economy and generation of biogas and therefore is considered as a promising solution for energy production from cheese whey, in this case. In this work, a comparative study between single and two-stage anaerobic treatment of cheese whey was conducted in order to enhance biogas production. Our experiments were carried out using one reactor for the single-stage process (operated at a HRT of 20 d), and two reactors connected in series, from which the first one was used for acidogenesis (operated at a HRT of 3 d) and the other for methanogenesis (operated at a HRT of 20 d). The single-stage process presented many operational problems, as a result of little or no buffering capacity of whey, which caused the pH of the anaerobic digester to drop drastically and the process being inhibited. This kind of inhibition proved to be irreversible and the digester was not able to recover even though it was operated batchwise and the value of the pH was restored to 7.0. On the contrary, the two-stage process exhibited a stable biogas production rate of 1.57 L/Lreactor/d with the composition of methane in the biogas reaching 54.3%. The dissolved COD and total carbon concentration removal was 70.5% and 77.2% respectively.