Chemical Methods for Hydrolyzing Dairy Manure Fiber: A Concise Review

Abstract

This paper reviews the chemical hydrolysis processes of dairy manure fiber to make its sugar accessible to microorganisms during anaerobic digestion and identifies obstacles and opportunities. Researchers, so far, investigated acid, alkali, sulfite, and advanced oxidation processes (such as hydrogen peroxide assisted by microwave/ultrasound irradiation, conventional boiling, and wet oxidation), or their combinations. Generally, dilute acid (3–10%) is less effective than concentrated acid (12.5–75%), which decrystallizes the cellulose. Excessive alkaline may produce difficult-to-degrade oxycellulose. Therefore, multi-step acid hydrolysis (without alkaline) is preferred. Such processes yielded 84% and 80% manure-to-glucose and -xylose conversion, respectively. Acid pretreatment increases lignin concentration in the treated manure and hinders subsequent enzymatic processes but is compatible with fungal cellulolytic enzymes which favor low pH. Manure high alkalinity affects dilute acid pretreatment and lowers glucose yield. Accordingly, the ratio of manure to the chemical agent and its initial concentration, reaction temperature and duration, and manure fineness need optimization because they affect the hydrolysis rate. Optimizing these factors or combining processes should balance removing hemicellulose and/or lignin and increasing cellulose concentrations while not hindering any subsequent process. The reviewed methods are neither economical nor integratable with the on-farm anaerobic digestion. Economic analysis and energy balance should be monolithic components of the research. More research is required to assess the effects of nitrogen content on these processes, optimize it, and determine if another pretreatment is necessary.

Evaluation of ammonia pretreatment of four fibrous biowastes and its effect on black soldier fly larvae rearing performance

“…These findings are consistent with values of 11 % DM protein, 81 % DM organic matter, and 58 % DM fiber previously reported by Gold et al (2020a). Cow manure is typically characterized by a high fiber content because it mainly consists of undigested animal feed and bedding material such as straw (Cata Saady et al, 2021).…”

Biochar from animal manure: A critical assessment on technical feasibility, economic viability, and ecological impact

“…Manure feedstocks mainly contain cellulose, hemicellulose, lignin, proteins, lipids and fats, and a substantial amount of nutrients. For example, birch wood is composed of 40% of cellulose, 26% of hemicellulose, and 16% of lignin (Mohan et al, 2006), and cattle manure contain 14%-35% of cellulose, 11%-32% of hemicellulose, and 13%-15% of lignin, 8%-30% of proteins, and 15%-32% of lipids and fats (Saady et al, 2021). During the pyrolysis, those compounds progressively break down with increasing pyrolysis temperature.…”