The effects of waste-activated sludge pretreatment using hydrodynamic cavitation for methane productionUltrasonics Sonochemistry

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Authors
Ilgyu Lee, Jong-In Han
Year
2013
DOI
10.1016/j.ultsonch.2013.03.006
Subject
Radiology Nuclear Medicine and imaging / Chemical Engineering (miscellaneous) / Acoustics and Ultrasonics

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Waste-activated sludge (WAS) tiva ge g p p W 120 s co at  2013 Elsevier B.V. All rights reserved.

Korea s rapi oks. Th the pr al with hydrolysis efficiency of waste-activated sludge (WAS) [5]. WAS mainly consists of microbial cells and extracellular polymeric substances (EPS), which are a complex mixture of proteins, polysaccharides, and lipids [6]. Microbial cell walls serve as sufficiently strong barriers that hinder the biodegradation of intracellular organics through the general AD process [7]. Pretreatment is to break the cell walls so that intracellular organics can be released careful analysis of overall cost [13,14]. Moreover, scaling-up for field applications is more of an issue [15].

Hydrodynamic cavitation (HC) exhibits similar effects to the ultrasonic method with greatly reduced energy consumption and thus, can be considered as a cost-effective substitute. Cavitation is generated, not from a sonication horn, but by forcing fluid flow through either a venturi tube or an orifice plate, where pressure substantially drops even to the level of vapor pressure. Many microbubbles are formed as a consequence of this pressure drop at the throat. These cavities subsequently collapse when the⇑ Corresponding author. Tel.: +82 42 350 3629; fax: +82 42 350 3610.

Ultrasonics Sonochemistry 20 (2013) 1450–1455

Contents lists available at o .e lE-mail addresses: jihan1968@gmail.com, hanj2@kaist.ac.kr (J.-I. Han).the potentially pathogenic, unstable, and irresoluble nature of the biosludge [1].

Disposal in sea or landfills, currently the most common practice for sludge management, gives rise to secondary pollution including leaching of heavy metals, nitrogen (N), and phosphorus (P) [2,3]. As a sustainable alternative, anaerobic digestion (AD) has been adopted to reduce sludge volume with the production of useful products, most notably methane. AD is now considered as an indispensable process in modernWWTPs [4], although some limitations do exist, such as long hydraulic retention time (HRT) and low ture above 150 C, but the production yield of methane was not improved [11]. Although alkaline pretreatment using NaOH, KOH, and Ca(OH)2 was reported to be comparatively efficacious in terms of sludge solubility, a high concentration of sodium or potassium ions inhibits AD. To minimize this negative effect, alkaline pretreatment is often combined with physical methods such as heating and sonication [12]. Ultrasound, a powerful physical method, produces high shear force via cavitation, making it possible to effectively disintegrate the sludge. However, the generation of ultrasound is energy intensive, and its application thus requiresAnaerobic digestion

Methane production 1. Introduction

Over the last 10 years in South water treatment plants (WWTPs) ha the water quality of rivers and bro however, has brought an increase in which must be treated before dispos1350-4177/$ - see front matter  2013 Elsevier B.V. A http://dx.doi.org/10.1016/j.ultsonch.2013.03.006, the number of waste dly increased to ensure is upsurge of WWTPs, oduced sewage sludge, additional cost, due to are thus typically required. These solubilized cell components are much more biodegradable and the HRT of the subsequent AD process becomes greatly shortened [8,9].

Various pretreatment methods have been developed to date.

Thermal pretreatment has been examined over an extensive range of temperatures from 50 to 200 C [10]. Sludge solubility was considerably enhanced by increasing the pretreatment tempera-Ultrasonication

Sludge pretreatment increased proportionally as WAS disintegration proceeded. HC, when combined with alkaline pretreatment, was found to be a cost-effective substitute to conventional methods for WAS pretreatment.The effects of waste-activated sludge pre cavitation for methane production

Ilgyu Lee, Jong-In Han ⇑

Department of Civil and Environmental Engineering, KAIST, 291 Daehak-ro, Yuseong-gu a r t i c l e i n f o

Article history:

Received 10 October 2012

Received in revised form 16 March 2013

Accepted 17 March 2013

Available online 6 April 2013

Keywords:

Hydrodynamic cavitation a b s t r a c t

Disintegration of waste-ac (AD) process to reduce slud shares a similar underlyin physical means to break u (72,000 kJ/kg TS), HC (60– was observed when HC wa used as alkaline catalysts

Ultrasonics S journal homepage: wwwll rights reserved.eatment using hydrodynamic ejeon 305-701, Republic of Korea ted sludge (WAS) is regarded as a prerequisite of the anaerobic digestion volume and increase methane yield. Hydrodynamic cavitation (HC), which rinciple with ultrasonication but is energy-efficient, was employed as a

AS. Compared with ultrasonic (180–3600 kJ/kg TS) and thermal methods 0 kJ/kg TS) found to consume significantly low power. A synergetic effect mbined with alkaline treatment in which NaOH, KOH, and Ca(OH)2 were pH ranging from 8 to 13. As expected, the production yield of CH4 gas

SciVerse ScienceDirect nochemistry sevier .com/ locate/ul tson

Fig. 1. Schematic representation of the hydrocavitator.

I. Lee, J.-I. Han /Ultrasonics Sonochpressure is restored downstream of the mechanical contraction. A number of studies have been conducted on various application targets, including cell disintegration, polymerization, and hydrolysis and transesterification of fatty oil [16–18].

The primary goal of this study is to obtain the optimal conditions for sludge pretreatment using HC for the purpose of maximum methane production from WAS. To improve the efficacy of sludge disintegration, another pretreatment approach, i.e., alkaline treatment was combined with HC, and their synergetic effects were examined, in terms of the release of COD, protein, total nitrogen (TN), and total phosphate (TP) and the production of methane. 2. Materials and methods 2.1. Waste-activated sludge (WAS) and anaerobic granular sludge

WAS was obtained from a final settling basin of a municipal

Waste Water Treatment Plant (WWTP) in Daejeon, South Korea.