Series of Combined Pretreatment Can Affect the Solubilization of Waste-Activated Sludge

Abstract

Various pretreatment methods have been combined and employed for maximizing the solubilization of waste-activated sludge (WAS). However, the question “by changing the series of applied combined pretreatments (CPs), can the solubilization efficiency of WAS be affected?” has never been addressed. In this study, firstly, thermal (T), alkaline (A), and ultrasonic (U) pretreatments were individually applied at broad strengths (T = 80–120 °C for 30 min, A = pH 9–12, and U = 5–60 min at 300 W). Then, pretreatment conditions that caused similar solubilization (13.0%) (120 °C, pH 11, and 30 min for T, A, and U, respectively), were adopted for CP with reverse sequences of T&A, U&A, and T&U. A similar disintegration degree was observed in U→A and A→U, while a meaningful difference was found in T&A and T&U: T→A (28.3%), A→T (42.9%), T→U (22.9%), and U→T (27.1%). The difference in pretreatment series also affected the characteristics of soluble matters, which was analyzed by excitation emission matrix and molecular weight distribution. Due to these differences, the highest methane yield of 68.8% (based on (chemical oxygen demand) CODinput) was achieved at A→T, compared to T→A (62.3%). Our results suggested a simple strategy for increasing solubilization, at the same expense of energy, which might be beneficial in the following treatment process, such as dewatering and transportation.

A Comprehensive Review on Pretreatment Methods for Enhanced Biogas Production from Sewage Sludge

“…Although the pretreatment methods are commonly applied individually as standalone procedures, the sequential or simultaneous application of some different methods has also been scrutinized [9]. The combined pretreatment has been of high popularity owing to better efficiencies in terms of sludge hydrolysis, solubilization of organic constituents, biogas and methane yield, compared to when these methods are applied alone [54,161,[200][201][202]. Additionally, coupling of single pretreatments in some cases, enables the improvement of some limitations that occur during the implementation of individual methods, which are usually associated with increased energy consumption, high capital, investment and operation costs [12].…”

“…The order the pretreatment methods are applied also affects the overall effectiveness. In the study of Mostafa et al [201], it was demonstrated that by altering the sequence of thermal-ultrasonic pretreatment set, solubilization was positively affected, presenting a surplus increment of 4%. That was assigned to ultrasonication, which led to a bulkier solids content than that resulted when it was not applied prior to thermal pretreatment, thereby increasing the availability of compounds for heating.…”

Perspectives on Potential Applications of Nanometal Derivatives in Gaseous Bioenergy Pathways: Mechanisms, Life Cycle, and Toxicity

“…With the agreement of the sustainable development goals (SDGs) adopted by the United Nations (UN), all ecofriendly waste treatment technologies have come under the spotlight . The production of methane (CH 4 ) and hydrogen (H 2 ) from organic-containing waste/wastewater, through anaerobic digestion (AD) and dark fermentation (DF) processes, is widely perceived as an efficient and sustainable treatment strategy promoting bioenergy recovery. − Basic knowledge about AD and DF often refers to their drawbacks, i.e., slow microbial growth and limited substrate conversion efficiency, respectively. − However, nanosized metal derivatives (NMDs), i.e., nanosized metals and their oxides, have unique chemical, thermal, and electrical properties that promote reaction yields . Nanosized provides a high surface to volume ratio and leads to totally different physicochemical properties compared to the corresponding material in its bulk size .…”

“…Formed NPs were washed twice using deionized water and finally were redispersed in cyclohexane.4 -Silica-coated n-Fe 3 nonylphenyl ether (Igepal CO-520) and cyclohexane were mixed using a mechanical stirrer for 15 min, and then oleic acid-coated n-Fe 3 O 4 (0.5 wt % in cyclohexane) was added. Finally, NH4 OH solution and tetraethyl orthosilicate (TEOS) were added consecutively under stirring, forming a transparent red solution of reverse microemulsion. A period of 16 h was required for completing this reaction.…”

Pilot-Scale Airlift Bioreactor with Function-Enhanced Microbes for the Reduction of Refinery Excess Sludge

“…Refinery excess sludge (RES) accounts for 0.3-0.5% of the total treatment wastewater quantity, the moisture content is usually approximately 95%, and the production in China is 300 × 10 4 t/y [2]. Moreover, the cost of sewage sludge treatment and disposal is over half of the total cost of wastewater treatment plants [3]. The sludge usually contains considerable amounts of toxic and harmful substances, such as parasite eggs, pathogenic microorganisms, heavy metals, and unstabilized organic matter [4,5].…”