Thermal Alkaline Hydrolysis Research Articles

Intracellular and Extracellular Sources, Transformation Process and Resource Recovery Value of Proteins Extracted from Wastewater Treatment Sludge Via Alkaline Thermal Hydrolysis and Enzymatic Hydrolysis

Intracellular and Extracellular Sources, Transformation Process and Resource Recovery Value of Proteins Extracted from Wastewater Treatment Sludge Via Alkaline Thermal Hydrolysis and Enzymatic Hydrolysis

Protein extraction from different sludge types by alkaline-thermal hydrolysis

Protein extraction from different sludge types by alkaline-thermal hydrolysis

Alkaline Thermal Hydrolysis of Sludge: Browning Reactions and Their Influence on Anaerobic Digestion and Protein Recovery

Alkaline Thermal Hydrolysis of Sludge: Browning Reactions and Their Influence on Anaerobic Digestion and Protein Recovery

Inhibition of Maillard reaction during alkaline thermal hydrolysis of sludge

The Maillard reaction (MR) occurs during the alkaline thermal hydrolysis (ATH) of sludge, which affects the quantity and quality of recovered protein. In this paper, four different sulfites were added to investigate their inhibitory effects on melanoidin production. The results showed that sulfites inhibited melanoidin production during ATH of sludge and the inhibitory rate increased with their concentration. At a concentration of 5.71 g/L, the inhibitory rates of NaHSO3 on melanoidin were 63.27%. Furthermore, the 3D-EEM (Three-Dimension Excitation-Emission-Matrix) fluorescence spectroscopy and protein testing data showed that the inhibition of melanoidin production was accompanied by an increased protein concentration, and protein increased with increasing sulfites concentration. A 2.5-fold increase in protein concentration with Na2S2O4 significantly enhanced the quantity of protein recovered. Therefore, the addition of sulfite during ATH of sludge reduces the amount of non-biodegradable melanoidin, which in turn benefits protein recovery.

Enhancing the removal efficiency of methylene blue in water by fly ash via a modified adsorbent with alkaline thermal hydrolysis treatment.

An effective adsorbent of methylene blue was synthesized from coal fly ash (FA; waste material from a coal power plant) by a denaturing process with an alkaline solution at 90 °C. The denatured fly ash (D-FA) has a surface area and pore volume of 66.39 m2 g−1 and 15.33 cm3 g−1, respectively, whereas the values of the original FA are negligible, i.e., 3.55 m2 g−1 and 0.02 cm3 g−1. The removal of methylene blue (MB) in aqueous solution by D-FA was increased in the range of initial MB concentration (10–20 mg L−1); contact time (0–120 min); pH (2–8); D-FA dosage (1–4 g L−1). However, a larger value of those operational parameters would not improve the removal activity. Furthermore, the methylene blue adsorption on the denatured FA was fitted with the Langmuir model with R2 = 0.9991; the maximum adsorption capacity was determined as 28.65 mg g−1 from the model. Overall, the highest removal efficiency of MB using D-FA with the dosage of 4 g L−1 was 97.1% in 30 mg L−1 solution of methylene blue at pH = 7. The alkaline hydrothermal denaturation of waste FA is a promising approach to produce an adsorbent with beneficial environmental engineering applications.

Microbial fuel cell-driven alkaline thermal hydrolysis for pretreatment of wastewater containing high concentrations of tetracycline in the cathode chamber

Wastewater containing high concentrations of antibiotics may inhibit the biological treatment processes, and it could also result in an increase in antibiotic resistant genes in the biological treatment system, causing risks in the environmental waters. Therefore, in this study, taking advantage of the unstable characteristics of tetracycline in alkaline conditions, dual-chamber microbial fuel cells (MFCs) were coupled with the heater to drive the alkaline thermal hydrolysis of tetracycline in the cathode chamber, making tetracycline degradation without contact with microorganisms in the anode chamber. It was observed that tetracycline degradation rates under closed circuit conditions were faster than those under open circuit conditions due to the rising pH in the cathode chamber of closed circuit MFCs, and the temperature increase could result in a decrease in half-life of tetracycline degradation. The TOC analysis showed that most TOC was not removed after 48 h reaction, suggesting tetracycline was mainly transformed to byproducts in the cathode chamber. High resolution mass spectrometry identified the transformation products resulting from the alkaline thermal hydrolysis of tetracycline, and the minimum pharmacophore of tetracycline was altered, which would lead to the loss of antibacterial activity. Microtox tests confirmed the reduction in the toxic effect of tetracycline to luminescent bacteria after treatment in the cathode chamber. Our results have demonstrated the effective degradation of tetracycline using MFC-driven alkaline thermal hydrolysis, which will have potential to be a pretreatment process to assist the subsequent biological treatment processes to destroy high concentrations of antibiotics in the wastewater.

Enhanced biological phosphorus removal using thermal alkaline hydrolyzed municipal wastewater biosolids

This study reports the feasibility of using municipal wastewater biosolids as an alternative carbon source for biological phosphorus removal. The biosolids were treated by a low-temperature, thermal alkaline hydrolysis process patented by Lystek International Inc. (Cambridge, ON, Canada) to produce short-chain volatile fatty acids and other readily biodegradable organics. Two sequencing batch reactors (SBRs) were operated with synthetic volatile fatty acids (SynVFA) and readily biodegradable organics produced from the alkaline hydrolysis of municipal wastewater biosolids (Lystek) as the carbon source, respectively. Municipal wastewaters with different strengths and COD:N:P ratios were tested in the study. The reactors' performances were compared with respect to nitrogen and phosphorus removal. It was observed that phosphorus removal efficiencies were between 98%–99% and 90%–97% and nitrogen removal efficiencies were 78%–81%, and 67% for the SynVFA and Lystek, respectively. However, the kinetics for phosphorus release and uptake during the anaerobic and aerobic stages with Lystek were observed to be significantly lower than SynVFA due to the presence of higher order VFAs (C4 and above) and other fermentable organics in the Lystek.

Kinetics of activated sludge protein extraction by thermal alkaline treatment

In order to explore an effective method to enhance application of activated sludge, kinetic model to describe extraction process of sludge protein was investigated based on experimental results. Relative molecular mass of sludge protein was tested using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that the extraction mechanism of sludge protein under thermal alkaline hydrolysis condition was in line with first-order continuous reaction kinetics. The kinetic model was established to explain relationships among first-order rate constant, pH value, and temperature. The optimum conditions were sludge retention time of 21d, extraction time of 2h, pH of 12, and temperature of 130°C. The extraction yield of sludge protein was 69% under the optimized conditions. Relatively molecular mass of sludge protein was between 26.478kDa and 430.86kDa, and the protein could be used as an excellent foaming agent.

Stepwise hydrolysis to improve carbon releasing efficiency from sludge

Based on thermal alkaline hydrolysis (TAH), a novel strategy of stepwise hydrolysis was developed to improve carbon releasing efficiency from waste activated sludge (WAS). By stepwise increasing hydrolysis intensity, conventional sludge hydrolysis (the control) was divided into four stages for separately recovering sludge carbon sources with different bonding strengths, namely stage 1 (60 °C, pH 6.0–8.0), stage 2 (80 °C, pH 6.0–8.0), stage 3 (80 °C, pH 10.0) and stage 4 (90 °C, pH 12.0). Results indicate stepwise hydrolysis could enhance the amount of released soluble chemical oxygen demand (SCOD) for almost 2 times, from 7200 to 14,693 mg/L, and the released carbon presented better biodegradability, with BOD/COD of 0.47 and volatile fatty acids (VFAs) yield of 0.37 g VFAs/g SCOD via anaerobic fermentation. Moreover, stepwise hydrolysis also improved the dewaterability of hydrolyzed sludge, capillary suction time (CST) reducing from 2500 to 1600 s. Economic assessment indicates stepwise hydrolysis shows less alkali demand and lower thermal energy consumption than those of the control. Furthermore, results of this study help support the concepts of improving carbon recovery in wastewater by manipulating WAS composition and the idea of classifiably recovering the nutrients in WAS.

Treatment of waste activated sludge by means of alkaline hydrolysis under mild conditions

Proper strategies for reducing the sludge production are a key factor for a correct wastewater treatment plant (WWTP) management. This paper describes an experimental study on sludge thermal alkaline hydrolysis under mild conditions (temperatures from 40 to 70 °C and pH up to 11.5), aimed at sludge minimisation. Tested biological sludge derived from two different WWTPs that treat urban and mixed urban/industrial wastewater, respectively. The experimental results showed: 1) an increase of soluble COD in sludge supernatants; 2) very good biodegradability of the supernatants; 3) improved settleability and dewaterability of treated sludge. The best results were obtained under the following conditions, using lime milk: 70°C, pH 10.0-10.5, contact time 3h.

Alkaline and acid thermal hydrolysis of biological excess sludge in sequencing batch reactor

The efficiency of biological wastewater treatment processes is based on pH sensitivity which leads to the reduction in the amount of sludge production. In order to achieve the best result, thermal hydrolysis is recognized and used, although acid thermal hydrolysis has serious drawbacks (corrosion, required post-neutralization, etc.). Alkaline thermal hydrolysis has been less remarkable, as the subject of the detailed pilot-scale research of two sequencing batch reactors (SBR) reported in this study. Long-term (about 8 months) continuous experiments were conducted to identify the effect of pH increasing from 4 to 11 in controlled temperature of 60°C to achieve the optimum pH for the reduction of excess biological sludge. After providing a steady state in the reactors, sampling and testing parameters including chemical oxygen demand (COD), mixed liquor suspended solids (MLSS), dissolved oxygen (DO), specific oxygen uptake rate (SOUR), sludge volume index (SVI), and yield (Y) coefficient were evaluated. Results showed that in pH of 9, the kinetic yield coefficient decreased from 0.63 to 0.33. Therefore, excess sludge declined to 44%. Moreover, the soluble COD increased slightly in the effluent, whereas the removal percentage decreased to 79 in the reactor while the amount of SVI and SOUR in this pH dropped to 65 mg/l and 12 mgO2/l.g VSS, respectively. However, no sludge was seen in the higher pH or lower pH, whereas effluent soluble chemical oxygen demand (SCOD) and turbidity was increased. Additionally, the wastewater disposal standards were not achieved and had a bad odor.

Enhanced volatile fatty acid production by a modified biological pretreatment in anaerobic fermentation of waste activated sludge

A novel protease/EDTA-2Na hydrolysis (PEH) pretreatment method was developed with the combination of EDTA-2Na hydrolysis (EH) and protease hydrolysis (PH) to improve volatile fatty acids (VFAs) production by anaerobic fermentation of waste activated sludge (WAS). Efficiencies of PEH, PH, EH and thermal alkaline hydrolysis (TAH) were compared in releasing SCOD from WAS. Results indicated that physicochemical pretreatment, TAH, had higher SCOD release but less utilization rate of the released SCOD in anaerobic fermentation, biological pretreatments, PH, showed less SCOD release but higher SCOD utilization rate, and PEH could simultaneously obtain higher SCOD release and utilization rate. By TAH, released SCOD could reach 19,273.21mg/l, but VFAs was only 11,820.36mg COD/L. By PEH, SCOD and VFAs were 13,628.98 and 12,704.44mg COD/L, respectively. SCOD released by PEH showed good biodegradability with BOD5/COD of 0.64%, 25.49% higher than that of TAH. By anaerobic fermentation, volatile suspended solids (VSS) of WAS pretreated by PEH could be reduced by 18.50%, but only 6.16% for TAH treated WAS. In PEH process, synergistic effects between protease and EDTA-2Na were observed, in which EDTA-2Na prevented protease from being trapped on the surfaces of sludge floccules and finally greatly improved protease efficiency. Therefore, it is feasible to apply PEH on enhancing VFAs production in anaerobic fermentation of WAS due to its higher and better bio-available carbon release than other pretreatments.

Enhanced nitrogen removal in a wastewater treatment process characterized by carbon source manipulation with biological adsorption and sludge hydrolysis

An innovative adsorption/nitrification/denitrification/sludge-hydrolysis wastewater treatment process (ENRS) characterized by carbon source manipulation with a biological adsorption unit and a sludge hydrolysis unit was developed to enhance nitrogen removal and reduce sludge production for municipal wastewater treatment. The system presented good performance in pollutants removal, yielding the effluent with average COD, NH4+-N, TN and TP of 48.5, 0.6, 13.2 and 1.0mg/L, respectively. Sixty percent of the total carbon source in the influent was concentrated and separated by the quick adsorption of activated sludge, providing the possibilities of reusing waste carbon source in the denitrification tank and accumulating nitrobacteria in the nitrification tank. Low temperature of 6–15°C and high hydraulic loading rate of 3.0–15.0m3/d did not affect NH4+-N removal performance, yielding the NH4+-N of lower 1.0mg/L in the effluent. Furthermore, 50% of the residual sludge in the ENRS system could be transformed into soluble COD (SCOD) by alkaline thermal hydrolysis with temperature of 60°C and pH of 11, and the hydrolyzed carbon could completely substitute methanol as a good quality carbon to support high efficient denitrification.

Degradation of endocrine disrupting bisphenol A during pre-treatment and biotransformation of wastewater sludge

The effect of various pre-treatment methods, including alkaline hydrolysis (AH), thermal hydrolysis (TH), thermal alkaline hydrolysis (TAH), thermal oxidation (TO) and thermal alkaline oxidation (TAO), on solubilization and simultaneous degradation of bisphenol A (BPA), an endocrine disruptor, in wastewater sludge (WWS) were investigated. The results showed that among AH, TH and TAH pre-treatments, TAH significantly improved the solubilization of WWS (41.6% suspended solid (SS), 70.7% volatile suspended solid (VSS) and 48.5% chemical oxygen demand (COD)) with higher degradation of BPA (38.4%). SS, VSS and COD solubilization were observed to be lower in TO and TAO pre-treatment as compared to TAH pre-treatment. However, higher degradation of BPA (75.0% and 78.9%) was observed in TO and TAO pre-treatment due to the presence of oxidation process. The effects of rheology and zeta potential on degradation of BPA in raw sludge and different pre-treated sludges were also investigated. The results showed that decrease in viscosity and particle size and increase in zeta potential resulted in higher degradation of BPA. BPA degradation by laccases produced by Sinorhizobium meliloti in raw and pre-treated sludge was also determined. Higher activity of laccases (230.9 U L −1) was observed in TAH pre-treated sludge resulting in high degradation of BPA (21.9%) suggesting concomitant biological degradation of BPA.

Recycling of excess sludge using titanium tetrachloride (TiCl 4) as a flocculant aid with alkaline-thermal hydrolysis

The highly strengthened treatment and disposal of excess sludge based on economic and environmental regulation factors is one of the important issues to be dealt with in the activated sludge process. In this study, the reduction and recycling technology of excess sludge were investigated for the aim of achieving a zero emission of excess sludge produced from the activated sludge process using titanium tetrachloride (TiCl 4) as a flocculant aid with alkaline-thermal hydrolysis. Alkaline-thermal hydrolysis of excess sludge was obtained 73% and 40% reduction rate at pH 13 (60 8 °C) and pH 11 (60 8 °C), respectively. Flocculation was carried out using a Ti-salt flocculant and the collected sludge was dewatered and incinerated at 600 °C to produce TiO 2 nanoparticles. The amount of total suspended solids and volatile suspended solids was significantly decreased with pH increase. The optimal dose of Ti-salt flocculation aid to improve dewatering ability of sludge breakage was 23.95 Ti-mg l −1. Also, in the batch culture, the supernatant after flocculation and the organic matter released from the lysed sludge were found to be useful as a source of energy for the growth of microorganisms during the aerobic operations period. TiO 2 produced from Ti-salt flocculation of excess sludge (TES) was characterized by X-ray diffraction, scanning electron microscopy/energy dispersive X-ray and photocatalytic activity.

Enhancing the use of waste activated sludge as bio-fuel through selectively reducing its heavy metal content

Power plant or cement kiln co-incineration are important disposal routes for the large amounts of waste activated sludge (WAS) which are generated annually. The presence of significant amounts of heavy metals in the sludge however poses serious problems since they are partly emitted with the flue gases (and collected in the flue gas dedusting) and partly incorporated in the ashes of the incinerator: in both cases, the disposal or reuse of the fly ash and bottom ashes can be jeopardized since subsequent leaching in landfill disposal can occur, or their “pozzolanic” incorporation in cement cannot be applied. The present paper studies some physicochemical methods for reducing the heavy metal content of WAS. The used techniques include acid and alkaline thermal hydrolysis and Fenton's peroxidation. By degrading the extracellular polymeric substances, binding sites for a large amount of heavy metals, the latter are released into the sludge water. The behaviour of several heavy metals (Cd, Cr, Cu, Hg, Pb, Ni, Zn) was assessed in laboratory tests. Results of these show a significant reduction of most heavy metals.

Reducing the Heavy Metal Content of Sewage Sludge by Advanced Sludge Treatment Methods

Waste-activated sludge (WAS) processes are key technologies to treat wastewater: their effluents can meet stringent discharge standards, thus ensuring a minimum residual impact on the aquatic environment. The presence of heavy metals in the excess sludge poses, however, serious problems, and considerably hampers the final disposal alternatives, especially in the agricultural use (soil improvement/amendment). This article studies the effect of thermal hydrolysis and Fenton's peroxidation on the heavy metal content of the dewatered sludge. Acid thermal hydrolysis reduces the heavy metal content in the filter cake except for Cu, Hg, and Pb. Alkaline thermal hydrolysis releases Cu, Pb, and Cr. Fenton's peroxidation transfers Cd, Cu, and Ni from the filter cake into the filtrate. Land application of the residual cake can hence be reconsidered.

Alkaline thermal sludge hydrolysis

The waste activated sludge (WAS) treatment of wastewater produces excess sludge which needs further treatment prior to disposal or incineration. A reduction in the amount of excess sludge produced, and the increased dewaterability of the sludge are, therefore, subject of renewed attention and research. A lot of research covers the nature of the sludge solids and associated water. An improved dewaterability requires the disruption of the sludge cell structure. Previous investigations are reviewed in the paper. Thermal hydrolysis is recognized as having the best potential to meet the objectives and acid thermal hydrolysis is most frequently used, despite its serious drawbacks (corrosion, required post-neutralization, solubilization of heavy metals and phosphates, etc.). Alkaline thermal hydrolysis has been studied to a lesser extent, and is the subject of the detailed laboratory-scale research reported in this paper. After assessing the effect of monovalent/divalent cations (respectively, K +/Na + and Ca 2+/Mg 2+) on the sludge dewaterability, only the use of Ca 2+ appears to offer the best solution. The lesser effects of K +, Na + and Mg 2+ confirm previous experimental findings. As a result of the experimental investigations, it can be concluded that alkaline thermal hydrolysis using Ca(OH) 2 is efficient in reducing the residual sludge amounts and in improving the dewaterability. The objectives are fully met at a temperature of 100 °C; at a pH≈10 and for a 60-min reaction time, where all pathogens are moreover killed. Under these optimum conditions, the rate of mechanical dewatering increases (the capillary suction time (CST) value is decreased from approximately 34 s for the initial untreated sample to approximately 22 s for the hydrolyzed sludge sample) and the amount of DS to be dewatered is reduced to approximately 60% of the initial untreated amount. The DS-content of the dewatered cake will be increased from 28 (untreated) to 46%. Finally, the mass and energy balances of a wastewater treatment plant with/without advanced sludge treatment (AST) are compared. The data clearly illustrate the benefits of using an alkaline AST-step in the system.