Use of trace elements addition for anaerobic digestion of brewer's spent grains.

The brewery industry generates a large amount of by-products and notably Brewer's Spent Grain (BSG) which seems an attractive substrate for anaerobic digestion. Nevertheless, previous studies have shown risk of inhibition in the mono-digestion of lignocellulosic substrates. One way to stabilize the reaction is the addition of trace elements. The current study evaluates and compares the stability of BSG anaerobic mono-digestion with and without addition of trace elements for several BSG samples. Based on the average composition of the BSG, two levels of nutrients addition were defined and tested on 4 different BSG samples. Control reactors, without addition of nutrients, showed signs of instability after 3 months or less of operation, with a decrease in performance and even collapse. On the contrary, supplemented reactors led to a COD removal rate of 60-65% and a methane production ranged between 220 and 350 NL CH4.kg-1 VSadded, depending on the sample. According to these results, guidelines for nutrients solution addition adapted to BSG degradation were defined.

Towards a standardization of biomethane potential tests.

Production of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. Although several norms and guidelines for BMP tests exist, inter-laboratory tests regularly show high variability of BMPs for the same substrate. A workshop was held in June 2015, in Leysin, Switzerland, with over 40 attendees from 30 laboratories around the world, to agree on common solutions to the conundrum of inconsistent BMP test results. This paper presents the consensus of the intense roundtable discussions and cross-comparison of methodologies used in respective laboratories. Compulsory elements for the validation of BMP results were defined. They include the minimal number of replicates, the request to carry out blank and positive control assays, a criterion for the test duration, details on BMP calculation, and last but not least criteria for rejection of the BMP tests. Finally, recommendations on items that strongly influence the outcome of BMP tests such as inoculum characteristics, substrate preparation, test setup, and data analysis are presented to increase the probability of obtaining validated and reproducible results.

Anaerobic digestion of Brewery Spent Grains: Trace elements addition requirement.

The current study evaluates and compares the stability of anaerobic digestion of Brewery Spent Grains (BSG) with and without addition of nutrients. Based on the composition of the BSG two levels of nutrients addition were defined. Control reactor, without addition of nutrients, showed signs of instability after 3months of operation and collapsed. On the contrary, supplemented reactors led to a COD removal rate of 60% and a methane production of 280NLCH4.kg-1 VSadded. According to these results, it was possible to define an additive solution adapted to BSG degradation.

Impact of initial biodegradability on sludge anaerobic digestion enhancement by thermal pretreatment.

Thermal treatments with temperature ranging from 60 to 210 degrees C were applied to 6 waste-activated sludge samples originating from high or medium load, extended aeration wastewater treatment processes that treated different wastewaters (urban, urban and industrial or slaughterhouse). COD sludge solubilisation was linearly correlated with the treatment temperature on the whole temperature range and independently of the sludge samples. Sludge batch mesophilic biodegradability increased with treatment temperature up to 190 degrees C. In this temperature range, biodegradability enhancement or methane production increase by thermal hydrolysis was shown to be a function of sludge COD solubilisation but also of sludge initial biodegradability. The lower the initial biodegradability means the higher efficiency of thermal treatment.