# Enzymatic Activity in the Anaerobic Co-Digestion of Cavitated Coffee Waste and Sewage Sludge
###### Abstract
Frequently, to support the AcD process, different groups of enzymes are added to the pre-treatment of waste that promote hydrolysis by decomposing hemicellulose, lignins, polysaccharides and protein [15]. [PERSON] et al. [16] noted the interference of anaerobic fermentation processes of waste was dependent on the amount of hemicellulose and lignin in the cell walls, which form barriers and limit enzyme contact with cellulose and inhibit the hydrolysis of polysaccharide polymers into sugars. Therefore, the removal of lignocellulosic biomass by the addition of enzymes to AcD improves the decomposition of anaerobic digestion conditions and thus enhances the yield of methane [17]. However, as reported by [PERSON] et al. [18], enzymatic hydrolysis requires the use of expensive enzymes to decompose polysaccharide polymers into sugars and the results may not necessarily be satisfactory and cover the costs incurred. The most important enzymes responsible for the transformation of organic matter are considered to be \(\beta\)-glucosidase (decomposes cellulose into glucose), phosphatases (decompose organic forms of phosphorus), urease (decomposes urea), or protease (decomposes protein). As reported in the literature, an appropriate microorganism population is important in the AnD process, and its activity depends on the parameters of the environment, in which microbes occur [14; 17]. In the first stage of AnD, compounds with a high molecular weight, such as proteins, carbohydrates and lipids, are broken down and the microorganisms involved (strict and facultative anaerobes) release various groups of enzymes [13]. These support the decomposition of extracellular polymeric substances and cell walls release readily available organic material necessary for subsequent processes [19]. Moreover, during AnD, the bacterial flora is constantly reconstituted, decomposing the introduced biomass and transforming it into a mixture of gases consisting mainly of carbon dioxide and methane, as well as hydrogen, ammonia, hydrogen sulfide, and other compounds [14]. Depending on the composition of the feedstock, different microorganisms may be involved in transformations and significant changes in their enzymatic activity may also occur. Thus, for anaerobic co-digestion (AcD), which processes different types of substrates, each type requires an analysis in this area. The novelty of this research involves evaluating the enzymatic activity in the anaerobic co-digestion of hydrodynamically cavitated CW and municipal sewage sludge (SS) as well as its influence on AcD performance. Moreover, the changes in the heavy metal content after AcD of CW and SS was investigated. Thus far, such a multi-aspect study has not been performed. It should also be noted that such an evaluation has not been conducted for these substrates. Additionally, there is limited knowledge indicating the metabolic pathways involving functional enzymes that play important roles in the biotransformation of macromolecules and methane production in AD. Importantly, the obtained research results will allow for the presentation of changes occurring during the anaerobic decomposition of selected substrates. Moreover, the conducted analysis provides an indication of the mechanisms of changes occurring during the anaerobic decomposition of these waste types. Therefore, the obtained results will be of great significance to scientists.