Abstract
To reveal the effects of thermal hydrolysis (TH) pretreatment (THPT) on anaerobic digestion (AD) of protein-rich substrates, discarded tofu was chosen as the object, and its batch AD tests of tofu before and after being subjected to TH at gradually increasing organic loads were carried out and the AD process characteristics were compared; furthermore, its continuous AD tests without and with THPT were also conducted and the difference of the microbial community structures was investigated. The results showed that, during AD of protein-rich tofu with increase in the organic load, inhibition from severe acidification prior to accumulation of ammonia nitrogen (AN) occurred. THPT helped overcome the acidification inhibition present in batch AD of tofu at such a high TS content of 3.6%, to obtain the maximum methane yield rate of 589.39 ml·(gVS)−1. Continuous AD of protein-rich tofu heavily depended on ammonia-tolerant hydrogenotrophic methanogens and bacteria. The continuous AD processes acclimated by HT substrates seemed to be resistant to severe organic loads, by boosting growth of ammonia-tolerant microorganisms, above all methylotrophic methanogens such as the genera RumEnM2 and methanomassiliicoccus. The process response of continuous AD of HT tofu was hysteretic, suggesting that a sufficiently long adaptation period was required for stabilizing the AD system.
Highlights
In recent years, soybean protein, livestock, poultry breeding and dairy product, and meat product processing industries have been developing rapidly with the increasing demand for protein food all over the world, in China with a large population
The volume of the gas product was determined by the draining saturated salt water method: A conical bottle was firstly filled with saturated salt water and connected with a long tube and a short tube through its seal plug; when a certain amount of gas entered from the short tube into the conical bottle, the equivalent amount of liquid was discharged from the long tube, and the volume of saturated salt water was measured by a volumetric cylinder and recorded as the volume of gas
3.1.1 pH Change During Batch anaerobic digestion (AD) Without thermal hydrolysis pretreatment (THPT) In the AD system, the decrease of pH is mainly affected by the activity of acidogenic microorganisms
Summary
Soybean protein, livestock, poultry breeding and dairy product, and meat product processing industries have been developing rapidly with the increasing demand for protein food all over the world, in China with a large population. Protein-Rich Biowastes Digestion and better medical care, large quantities of protein-rich sludges were produced, with their annual output surpassing 30 million tons per year (Mateo-Sagasta et al, 2015). It is necessary and important to study the response of the AD system to excessive AN as well as the mitigation measures to the possible inhibition After all, it is necessary for some protein-rich substrates to be subjected to THPT, e.g., for municipal sludge containing protein granule substrate and high protein content EPSs to enhance their biochemical properties (Villamil et al, 2020), and for (several million tons of) antibiotic mycelial residues to eliminate inhibition of antibiotics left in them (Zhang et al, 2015). Note: SCOD, soluble chemical oxygen demand; TAN, total ammonia nitrogen; TS, total solid; VS, volatile solid
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