Abstract
Abstract Digestate from biogas plants, formed by dewatering anaerobically stabilized sludge, is characteristic of high concentrations of phosphates and ammonia nitrogen suitable for further use. Phosphorus is an element widely used to produce fertilizers, and because of its continually shortening natural supplies, recycling of phosphorus is gaining on significance. Both phosphorus and nitrogen are important elements and their presence affect the quality of water resources. Both elements can contribute to eutrophication. At the same time, both phosphorus and ammonia nitrogen, are important elements for agricultural production, and therefore greater demands are being made on the effort to connect sewage treatment processes and the process of recycling of these nutrients. A suitable product of phosphorus and ammonia nitrogen are phosphates in the form of a structurally-poorly soluble precipitate of magnesium ammonium phosphate (struvite). This form of slowly decomposing fertilizer is distinguished by its fertilizing abilities. Compared to direct use of digestate as a fertilizer, struvite is more stable and can gradually release ammonia nitrogen for a long time without unnecessary losses. In the reported experiments, the precipitation efficiency of the recycling of ammonia nitrogen and phosphorus from the digestate liqour (liquid discharge from digestate) was, at a stoichiometric ratio of Mg2+: NH4+: PO43− (3.2: 1: 0.8) and a stirring time of 15 minutes, 87 % for ammonia nitrogen ions.
Highlights
Digestate, a nutrient-rich material produced by anaerobic digestion at biogas plants, can be applied as a fertilizer
The processing of wastes listed in Czech Waste Act 185/2001 Coll and other materials stated by Regulation (EC) 1774/2002 of the European Parliament and of the Councilis is forbidden in agricultural biogas plants
Laboratory measurements were based on a chemical analysis of digestate liqour, which determined the concentrations of ammonia, phosphate, and magnesium ions
Summary
A nutrient-rich material produced by anaerobic digestion at biogas plants, can be applied as a fertilizer. The nutrients are extensively more available in digestate, meaning it is easier for plants to utilize them. The digestate handling options mainly depend on the resulting quality of the product generated after anaerobic digestion. This means that the way of disposal depends mainly on the properties of input raw materials entering the biogas plants [1]. The processing of wastes listed in Czech Waste Act 185/2001 Coll and other materials stated by Regulation (EC) 1774/2002 of the European Parliament and of the Councilis is forbidden in agricultural biogas plants. A common feature for digestate is low dry matter content, which for agricultural biogas plant, is between 2 and 9 %
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