The effect of the addition of novel alkali-activated material (AAM) granules to provide additional buffering capacity, pH stability and increased methane yields in batch scale anaerobic digestion was investigated.The experiments were carried out with 20%, 30% and 40% of acidic whey in 500 ml batch reactors by a single addition of AAM granules (diameter from 2 to 8 mm) at 37 ± 0.5x00B0;C during 30 days. Presence of the AAM in the batch reactors allowedto maintain optimal pH, thus increasingthe yield and rate of methane formation from acid whey.

This study was motivated by the need to make better use of animal protein from animal by-products (ABPs). The goal was to develop a tool to monitor and assess the production and use of ABP resources in cooperation with both companies and state authorities. Data was gathered from a wide variety of sources, and was used to determine the number of animals (by species) and yield of various types of ABPs categorized into risk categories produced per animal during meat processing. The reliability of this data was tested using both direct observation and by comparing with additional data sources. Only the number of animals of each species processed are required to estimate the quantities of the various types of ABPs produced within each risk category. During evaluation of the calculation-tool it was estimated that 22,741 tons of ABPs are generated in the slaughterhouses certified within Estonia annually. The quantity of ABPs delivered by meat processing plants for reprocessing as 1st category waste was 4888 tons in 2013. This total exceeds our estimate by ~3.5 times. We thus conclude that ABPs from lower risk categories are being sent for reprocessing as the highest risk-category of waste. This implies that the meat industry is making insufficient use ABPs as raw material. A strategy for developing a fully functional and efficient system to manage ABP recourses within slaughterhouses is discussed, and our tool, together with these ideas could be used to develop and implement such a plan within processing companies in other countries.

The Anaerobic Digestion Model No.1 (ADM1) was improved to simulate an anaerobic digestion start-up phase. To improve the ADM1, a combined hydrolysis equation was used based on the Contois model of bacterial growth and the function of hydrolysis inhibition by VFA. The start-up with fresh cattle slurry was carried out in a pilot-scale reactor to calibrate the chosen parameters of the ADM1. The important aspects of model calibration were hydrolysis rate, the number of anaerobic microbes in cattle slurry, and the growth rate of bacteria. Good simulation results were achieved after calibration for the independent start-up test with pre-conditioned cattle slurry.

Lipid and protein rich solid slaughterhouse wastes are attractive co-substrates to increase volumetric biogas production in co-digestion with dairy manure. Addition of decanter sludge (DS), containing 42.2% of lipids and 35.8% of proteins (total solids basis), up to 5% of feed mixture resulted in a stable process without any indication of long chain fatty acids (LCFA) or free ammonia (NH3) inhibition and in 3.5-fold increase of volumetric biogas production. Contrary, only lipids addition as technical fat (TF) at over 2% of feed mixture resulted in formation of floating granules (FG) and process efficiency decrease. Formed FG had low biodegradability and its organic part was composed of lipids and calcium salts of LCFAs. Anaerobic digestion process intentionally directed to FG formation, could be a viable option for mitigation and control of lipids overload and derived LCFA inhibition.

The rendering product of Category 2 and 3 Animal By-Products is known as sterilized mass (SM) and it is mainly composed of fat and proteins, making it interesting substrate for anaerobic digestion. Batch and semi-continuous laboratory experiments were carried out to investigate the effect of SM addition in co-digestion with sewage sludge on methane production and possible process limitations. Results showed that SM addition in the feed mixture up to 5% (w/w), corresponding to 68.1% of the organic loading, increased methane production 5.7 times, without any indication of process inhibition. Further increase of SM addition at 7.5% (w/w) caused methane production decrease and volatile solids removal reduction, that was mainly related to remarkably increased free ammonia concentration in the digester of 596.5±68.6 gNH3 L(-1). Sterilized mass addition of 10% (w/w) caused intensive foaming, LCFA accumulation of 9172±701.2 mgCOD-LCFA g(-1) sample and termination of the experiment.

The aim of the current study was to determine chemical composition and methane potential of Category 2 and 3 solid slaughterhouse wastes rendering products (SSHWRP) viz. melt, decanter sludge, meat and bone meal (MBM), technical fat and flotation sludge from wastewater treatment. Chemical analyses showed that SSHWRP were high in protein and lipids with total solids (TS) content of 96-99%. Methane yields of the SSHWRP were between 390 and 978 m(3) CH(4)/t volatile solids (VS)(added). Based on batch experiments, anaerobic digestion of SSHWRP from the dry rendering process could recover 4.6 times more primary energy than the energy required for the rendering process. Estonia has technological capacity to sterilize all the produced Category 2 and 3 solid slaughterhouse wastes (SSHW) and if separated from Category 1 animal by-products (ABP), it could be further utilized as energy rich input material for anaerobic digestion.