High‐Solids Anaerobic Digestion of Municipal Sludge Pretreated by Thermal Hydrolysis

Abstract

High‐solids anaerobic digestion can consistently achieve 55 to 60% volatile solids destruction after thermal hydrolysis pretreatment, which reduces its viscosity and increases the fraction of soluble organic matter. For feed sludge with total solids concentrations between 6.8 and 8.2%, the process is stable at hydraulic retention times of 9 to 12 days, significantly increasing the treatment capacity of existing digesters or, in treatment plants without spare capacity, helping to postpone, reduce, or even avoid costly infrastructure investments. Process stability is related to the high concentration of soluble organic matter in the digesters. High‐solids temperature‐phased digestion appears to be superior to high‐solids mesophilic digestion, with respect to process flexibility and stability, biosolids stabilization, and biogas generation, although ammonia inhibition may have occurred. Implementation of high‐solids digestion could significantly reduce operation and maintenance costs of solids‐handling operations.

Biogas production from low-organic-content sludge using a high-solids anaerobic digester with improved agitation

“…High-solids anaerobic digestion has been used to treat some kinds of organic wastes, such as the organic fraction of municipal solid waste [10,11,12], industrial wastes [13], yard waste [14], food waste [15], and agricultural wastes [16,17]. However, unlike these uncompacted wastes, sludge with a high solids content is a kind of pseudo-plastic fluid or sticky semisolid having very high viscosity, which can result in inefficient mixing and poor mass transfer efficiency [18]. In fact, without any agitation, the sludge with TS higher than 12% hardly produced any biogas in our preliminary experiments.…”

“…Thus far, only a few attempts have been made to produce biogas directly from sludge with TS higher than 10% in digesters that use agitation [8,15] or pretreatment [18,4,19]. These studies indicated that in anaerobic mono-digestion of high-solids sludge, the organic removal rate and the specific biogas production per VS added (SBP ad ) both decreased significantly at the same SRT used in conventional low-solids digesters, or the SRT had to be prolonged in order to achieve the same organic removal rate and SBP ad as in conventional low-solids digesters.…”

Effects of Thermal-Alkaline Pretreatment on Solubilisation and High-Solid Anaerobic Digestion of Dewatered Activated Sludge

“…Hence, high-solid anaerobic digestion (TS ≥ 15%) (Guendouz et al 2008) is a potential solution to the sludge disposal problem, as it avoids secondary sludge dehydration in low-solid anaerobic digestion. In addition, high-solid anaerobic digestion is advantageous because of its smaller reactor volume, lower energy input for heating, and less material handling (Domenec 2009;Duan et al 2012;Fernández Rodríguez et al 2012;Zhang et al 2015).…”

Status of anaerobic digestion pretreatment of high solid waste

“…After thermal hydrolysis pretreatment, which reduces sludge viscosity and increases the fraction of soluble COD, highsolids anaerobic digestion is stable, produces highly stabilized biosolids, and greatly increases biogas generation [4].…”