Abstract
Ammonia accumulation in biogas plants reactors is becoming more frequently encountered, resulting in reduced methane (CH4) production. Ammonia toxicity occurs when N-rich substrates represent a significant part of the biogas plant’s feedstock. The aim of this study was to develop an estimation method for the effect of ammonia toxicity on the CH4 production of biogas plants. Two periods where a biogas plant operated at 3200 mg·L−1 (1st period) and 4400 mg·L−1 (2nd period) of ammonium nitrogen (NH4+–N) were examined. Biomethane potentials (BMPs) of the individual substrates collected during these periods and of the mixture of substrates with the weight ratio used by the biogas plant under different ammonia levels (2000–5200 mg·L−1 NH4+–N) were determined. CH4 production calculated from the substrates’ BMPs and the quantities used of each substrate by the biogas plant was compared with actual CH4 production on-site. Biogas plant’s CH4 production was 9.9% lower in the 1st and 20.3% in the 2nd period in comparison with the BMP calculated CH4 production, of which 3% and 14% was due to ammonia toxicity, respectively. BMPs of the mixtures showed that the actual CH4 reduction rate of the biogas plant could be approximately estimated by the ammonia concentrations levels.
Highlights
Organic waste treatment technologies are becoming more and more inextricably linked to renewable energy production and they are an integral part of pollution reduction strategies and policies
The waste quantities introduced in the biogas reactor for each period, their CH4 potential and the calculated CH4 production based on the added quantity and the Biomethane potentials (BMPs)
The results of this study showed that is possible to estimate the CH4 reduction of a biogas plant caused by high ammonia concentrations depending on the nitrogen composition of the raw influent wastes
Summary
Organic waste treatment technologies are becoming more and more inextricably linked to renewable energy production and they are an integral part of pollution reduction strategies and policies. The biogas sector contributes a significant part of the renewable energy production in EU, an industry under rapid expansion as more than 18,000 plants were operating in 2019 in contrast with approximately 6000 in 2009 [1]. The availability of raw materials is directly related to the viability and profitability of biogas plants. The expected growth of the biogas sector will in some cases lead to a competition for the acquisition of raw materials from the same sources, affecting the viability of biogas plants [4]. An animal farm herd reduction or high acquisition prices for corn silage caused by market volatility will affect the biogas plant production. Raw materials transportation cost has a major impact on the operational expenses of the biogas plant and strongly influences the decision on whether a substrate will be utilized [5]
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