Multivariate analysis of sludge disintegration by microwave-hydrogen peroxide pretreatment process

Speciation evolution and transformation mechanism of P during microwave hydrothermal process of sewage sludge

Due to the global shortage of phosphate ore, sewage sludge is an important resource for P recovery. This study aims to investigate how P was migrated and transformed during the microwave hydrothermal (MHT) process of sewage sludge. The effects of MHT and hydrothermal (HT) conversion were compared. The results reveals that there were no significant differences on the P distribution and speciation changes between the HT and MHT products, especially under high hydrothermal temperature. Ortho-P/Pyro-P was the dominant P form in the hydrothermal solid products, and high temperature promoted the transformation of C-O-P to Ortho-P/Pyro-P. The analysis of X-ray absorption near edge structure (XANES) shows that Ca₅(PO₄)₃OH was formed after the hydrothermal processes. The relative abundance of Ca-P decreased first and then increased with increasing hydrothermal temperature. Moderate MHT temperature (170 °C) and holding time (30-60 min) promoted the transformation of P to the liquid products. Generally, the effect of MHT temperature was more significant than that of heating type and holding time on the variations of P distribution and speciations.

Insight into the fenton-induced degradation process of extracellular polymeric substances (EPS) extracted from activated sludge

Although EPS in microbial aggregates are importance in successful implementation of biological wastewater treatment systems, they also exhibit detrimental role on certain circumstance, such as excess sludge dewatering. Extensive efforts have been put into the disruption of EPS for improving the dewaterability of excess sludge and Fenton's reagent treatment has been demonstrated to be a very promising sludge conditioning method for EPS destruction. However, the information regarding detailed degradation process of EPS during Fenton's reagent treatment is limited. In this study, EPS were extracted from activated sludge and treated with different concentrations of Fenton's reagent. The physicochemical characteristic changes of EPS under different treatment were investigated in terms of components, EEM, molecular weight (MW), UV-Vis and FTIR. The results showed that EPS were prone to be disintegrated, but hard to be fully mineralized. Humic substances in EPS were more resistant to Fenton's reagent than other components. Low MW components of EPS were preferentially degraded prior to the disruption of high MW components. Besides, the disintegration of EPS into lower MW ones was accompanied by the formation of higher MW compounds caused by the bridge interaction of Fe ions. The cleavage of protein's backbone in EPS was mainly through destruction of amide II (N-H and C-N) in -CO-NH-. Fenton's reagent treatment also led to a significant increase of oxygen-containing functional groups in EPS molecules. This paper may pave a path to deeply understand the mechanisms of dewatering improvements of excess sludge by Fenton's conditioning.

Ultrahigh pressure filtration dewatering of municipal sludge based on microwave pretreatment

Municipal sludge is difficult to treat and dispose of because of its high moisture content (MC) and volume. In this study, a novel dewatering method that utilizes ultrahigh pressure filtration (UHPF) and thin-cake-press (TCP) coupled with microwave pretreatment was proposed to reduce the MC of sludge cake. The influence of microwave contact time (MCT), microwave intensity (MI), initial MC of sludge, dewatering time, applied pressure and sludge weight (Ws) on the MC of a sludge cake was investigated by the single-factor experiment. Moreover, a water discharge path model was developed to understand the dewatering mechanism and explain the relationship between thickness and MC of the cake. The key factors affecting the MC of the cake were explored by the orthogonal experiment. The experimental results showed that microwave irradiation could effectively improve the dewatering performance and reduce the MC of the sludge cake. The MC of the cake reached its lowest value of 28% at MCT of 120 s and MI of 400 W, which is much lower than the value obtained by the traditional dewatering method. Among the parameters mentioned above, Ws has the most significant influence on MC because a large amount of sludge leads to a thicker cake, which seriously hampers the flow of filtrate and inevitably increases the MC of the cake.

Carbon dioxide sequestration and methane production promotion by wollastonite in sludge anaerobic digestion

This study investigated the feasibility and performance of simultaneous in-situ CO₂ sequestration and CH₄ production promotion by wollastonite addition in sludge AD. A maximum CH₄ yield increment of 30.8% and maximum methane production rate increment of 64.9% with wollastonite addition at dosage of 16.25 g/L were achieved. CO₂ was efficient sequestered by wollastonite addition and resulted in a higher CH₄ content of 81.7%-82.4%. The mechanism of CO₂ sequestration by wollastonite was confirmed as Ca²⁺ release and subsequently carbonation based on cation and precipitates analysis. The results demonstrated that wollastonite could be applied as an effective additive for simultaneous in-situ CO₂ sequestration and CH₄ production promotion of sludge AD.

H2O2 induced cost effective microwave disintegration of dairy waste activated sludge in acidic environment for efficient biomethane generation

This study aimed to improve the biomethane potential of dairy waste activated sludge (WAS) by H₂O₂-acidic pH induced microwave disintegration (HAMW-D) pretreatment approach. The results of HAMW-D compared with the microwave disintegration (MW-D) alone for energy and economic factors. In the two phase disintegration process, the H₂O₂ concentration of about 0.5mg/g SS under acid pH of 5 was found to be optimum for effective dissociation of Extracellular Polymeric Substances (EPS) matrix. A higher liquefaction of about 46.6% was achieved in HAMW-D when compared to that of MW-D (30%). It subsequently improved the methane yield of about 250mL/g VS in HAMW-D, which was 9.6% higher than MW-D. A net profit of about 49€/ton was achieved for HAMW-D, therefore it is highly recommended for WAS pretreatment.

Optimization study on the hydrogen peroxide pretreatment and production of bioethanol from seaweed Ulva prolifera biomass

The seaweed Ulva prolifera, distributed in inter-tidal zones worldwide, contains a large percentage of cellulosic materials. The technical feasibility of using U. prolifera residue (UPR) obtained after extraction of polysaccharides as a renewable energy resource was investigated. An environment-friendly and economical pretreatment process was conducted using hydrogen peroxide. The hydrogen peroxide pretreatment improved the efficiency of enzymatic hydrolysis. The resulting yield of reducing sugar reached a maximum of 0.42g/g UPR under the optimal pretreatment condition (hydrogen peroxide 0.2%, 50°C, pH 4.0, 12h). The rate of conversion of reducing sugar in the concentrated hydrolysates to bioethanol reached 31.4% by Saccharomyces cerevisiae fermentation, which corresponds to 61.7% of the theoretical maximum yield. Compared with other reported traditional processes on Ulva biomass, the reducing sugar and bioethanol yield are substantially higher. Thus, hydrogen peroxide pretreatment is an effective enhancement of the process of bioethanol production from the seaweed U. prolifera.

Enhancement of sludge anaerobic biodegradability by combined microwave-H2O2 pretreatment in acidic conditions

The aim of this study was to increase the sludge disintegration and reduce the cost of microwave (MW) pretreatment. Thermodynamic analysis of MW hydrolysis revealed the best fit with a first-order kinetic model at a specific energy of 18,600 kJ/kg total solids (TS). Combining H2O2 with MW resulted in a significant increment in solubilization from 30 to 50 % at 18,600 kJ/kg TS. The pH of H2O2-assisted MW-pretreated sludge (MW + H2O2) was in the alkaline range (pH 9-10), and it made the sludge unfavorable for subsequent anaerobic digestion and inhibits methane production. In order to nullify the alkaline effect caused by the MW + H2O2 combination, the addition of acid was considered for pH adjustment. H2O2-assisted MW-pretreated sludge in acidic conditions (MW + H2O2 + acid) showed a maximum methane production of 323 mL/g volatile solids (VS) than others during anaerobic biodegradability. A cost analysis of this study reveals that MW + H2O2 + acid was the most economical method with a net profit of 59.90 €/t of sludge.

Effect of organic matter on phosphorus recovery from sewage sludge subjected to microwave hybrid pretreatment

Microwave (MW) hybrid processes are able to disrupt the flocculent structure of complex waste activated sludge, and help promote the recovery of phosphorus as struvite. In this study, to optimize struvite yield, (1) the characteristics of matter released in MW-hybrid treatments were compared, including MW, MW-acid, MW-alkali, MW-H2O2, and MW-H2O2-alkali. The results showed that selective release of carbon, nitrogen, phosphorus, Ca(2+), and Mg(2+) achieved by sludge pretreatment using MW-hybrid processes. MW-H2O2 is the recommended sludge pretreatment process for phosphorus recovery in the form of struvite. The ratio of Mg(2+):NH4(+)-N:PO4(3-)-P was 1.2:2.9:1 in the supernatant. (2) To clarify the effects of organic matter on struvite recovery, the composition and molecular weight distribution of organic matters were analyzed. Low molecular weight COD was found to facilitate the removal rate of NH4(+)-N and PO4(3)-P via crystallization, and the amorphous struvite crystals (<1kDa) from the filtered solutions had high purity. Therefore, the present study reveals the necessity of taking into consideration the interference effect of high molecular weight organic matters during struvite crystallization from sewage sludge.

Pilot-scale study of sludge pretreatment by microwave and sludge reduction based on lysis-cryptic growth

To evaluate the performance of microwave (MW)-chemical hybrid sludge treatment system, a pilot scale MW disintegration unit (treatment capacity of 500L/d) was constructed. The results showed that organic matter, nitrogen, and phosphorus were effectively released from the MW-pretreated sludge. The values of COD released were 15.91%, 15.07%, 13.83%, 19.35%, and 15.07% for the MW, MW-acid, MW-alkali, MW-H2O2, and MW-H2O2-alkali treatment processes, respectively. Additionally, for a wastewater treatment system with a capacity of 200m(3)/d, when coupled with a MW sludge pretreatment unit, the sludge production and sludge yield were greatly reduced by 38.60% and to 0.35kg VSS/kg CODconsumed, respectively. The total operating cost of the lysis-cryptic growth system was 13.64% lower than that of the CAS system without a MW unit.