Laboratory-scale biosolids dewaterability assessment for municipal water resource recovery facilities (original) (raw)
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PILOT-SCALE EVALUATION OF ENZYME PRE-TREATMENT TO ENHANCE DEWATERING: EFFECTS OF SHEAR AND POLYMER
Proceedings of the Water Environment Federation, 2007
The effect of enzyme pre-treatment on dewaterability of anaerobically digested biosolids was investigated at both laboratory and pilot scale. Similar to previously reported results, laboratory results revealed a significant increase in cake solid content (33% cake solids compared to 20% without enzyme pretreatment), using an enzyme dose of only 15 mg/L. In order to assess practical application, enzyme pre-treatment was applied at the Wilmington wastewater treatment plant, using a pilot-scale centrifuge. However, the dewatering efficiency reached in laboratory scale could not be obtained in pilot scale, where the final cake solids content reached only 20% with different enzyme doses. Possible factors that might cause the differences were tested by experimental and statistical comparisons. Results indicated that the higher shear applied in centrifugation is responsible for the lack of improved cake solids. The network strength of sludge determined by rheological measurements revealed that enzymatic treatment could weaken the gel structure of the sludge floc through the hydrolysis of extracellular polymeric substances; this allows improved dewatering by filtration processes, but leads to floc deterioration when subjected to high shear during centrifugation. Different polymers with different chemical structures were tested, however, only 2 pts increase in cake solids were observed in pilot centrifugation. Pilot or full scale testing with belt filter press devices is needed to verify the observed increase in cake solids with the Crown Press simulator.
CNash - A novel parameter predicting cake solids of dewatered digestates
Water Research, 2019
Efficient digestate dewatering is crucial to reduce the volume and transportation cost of solid residues from anaerobic digestion (AD) plants. Large variations in dewatered cake solids have been reported and predictive models are therefore important in design and operation of such plants. However, current predictive models lack validation across several digestion substrates, pre-treatments and full-scale plants. In this study, we showed that thermogravimetric analysis is a reliable prediction model for dewatered cake solids using digestates from 15 commercial full-scale plants. The tested digestates originated from different substrates, with and without the pre-AD thermal hydrolysis process (THP). Moreover, a novel combined physicochemical parameter (C/Nash) characterizing different digestate blends was identified by multiplying the C/N ratio with ash content of the dried solids. Using samples from 22 full-scale wastewater, food waste and co-waste plants, a linear relationship was found between C/Nash and predicted cake solids for digestates with and without pre-AD THP. Pre-AD THP improved predicted cake solids by increasing the amount of free water. However, solids characteristics like C/N ratio and ash content had a more profound influence on the predicted cake solids than pre-AD THP and type of dewatering device. Finally, C/Nash was shown to have a linear relationship to cake solids and reported polymer dose from eight full-scale pre-AD THP plants. In conclusion, we identified the novel parameter C/Nash which can be used to predict dewatered cake solids regardless of dewatering device and sludge origin.
Desalination and Water Treatment, 2016
This study aims to characterize anaerobically digested sludge (ADS) and correlate the sludge characteristics in terms of soluble organic compounds with polymer demand (PD) during sludge conditioning. The PD required to achieve maximum dewatering of the ADS studied is in the range of 8-10 kg polymer/dry ton. The commonly used capillary suction time parameter to evaluate the solid-liquid separation ability was not a reliable indicator for assessing dewatering. Instead, in this study, a modified centrifugal technique proposed by Higgins (Higgins MCT) was used to assess the maximum achievable dry solids content of the biosolids cake. The Higgins MCT is readily obtained using a bench-scale centrifuge equipped with a modified centrifuge bucket. Using the Higgins MCT, the maximum dry solids contents obtained from conditioned ADS was 30 wt%. These values were comparable to the dry solids content obtained from the same sludge at full-scale level. Our results suggest Higgins MCT is suitable for assessing the final dry solids content and simulating the dewatering process.
Water Science & Technology, 2006
The effect of enzyme pre-treatment on dewaterability of anaerobically digested sludge was investigated at both laboratory and pilot scale. Our results revealed a significant increase in cake solid content (27% cake solids compared to 18% without enzyme pretreatment), using an enzyme dose of only 20 mg/L. In order to assess practical application, enzyme pre-treatment was applied at the Wilmington, Delaware (U.S.) wastewater treatment plant, using a pilot-scale centrifuge. However, the efficiency reached in laboratory scale could not be obtained in pilot scale, where the final cake solids content did not exceed 20%. Centrifuge and belt filter press (simulated by Crown Press™) dewatering were compared in terms of the process efficiencies in the absence and presence of enzyme pre-treatment. Possible factors that might cause the differences were tested by experimental and statistical comparisons. Results indicated that the higher shear applied in centrifugation is responsible for the lack of improved cake solids. The network strength of sludge determined by rheological measurements revealed that enzymatic treatment weakens the gel structure of the sludge floc through the hydrolysis of extracellular polymeric substances; this allows improved dewatering by filtration processes, but leads to floc deterioration when subjected to high shear during centrifugation.
Empirical correlations for the prediction of cake dewatering characteristics
Minerals Engineering, 1989
The irreducible equilibrium saturation and dewatering kinetics of vacuus-dewatered filter cakes are studied. Limitations of available empirical correlations for cake dewatering characteristics are presented. The mechanisms of air displacement dewatering are delineated as no-air-flow and air-flow dewatering regimes, and new nondimensional groups combining the pertinent parameters in each regime are proposed for correlating the equilibrium saturation. On the basis of the capillary flow dynamics, a nondimensional group is formulated for the correlation of dewatering kinetics in the absence of air flow rate data. The correlations are verified with the experimental data obtained from the filtration of hematite slurries and an empirical equation based on the same data is suggested for equilibrium saturation predictions.
2011
A series of belt filter press trials were performed to assess BFP technology as a method for dewatering digested biosolids which had been pretreated by the Cambi Thermal Hydrolysis Process (THP). The THP is a sludge pretreatment process which heats raw sludges to high temperature (150-165 °C) using steam followed by mesophilic digestion. In this study, two different full scale THP sludges were dewatered on two belt filter presses supplied by two different manufacturers. The digested THP sludges had solids concentrations between about 5-7%. The goal of the project was to evaluate the effect of solids loading rates and polymer dosing on cake solids and capture. The results showed the THP sludges dewatered well using BFPs, with cakes solids of 30% or higher easily achieved along with capture rates greater than 99%. This performance was achieved over a broad solids loading rate with 30% cake solids being achieved at loading rates of up to 1000 kg/m-hr. The study also showed that mixing of the polymer and sludge was a critical parameter for achieving good flocculation and dewatering.
Investigations Into Improving Dewaterability at a Bio-P/Anaerobic Digestion Plant
Water environment research : a research publication of the Water Environment Federation, 2016
Metropolitan Council Environmental Services has observed poorer than expected dewatering performance at its Empire Plant. This plant has both anaerobic digestion and enhanced biological phosphorus removal in its treatment train. A research program using pilot scale anaerobic digesters, investigated potential solutions to the plant's poor dewaterability. The dewaterability goal was to increase the cake solids from 12% total solids (TS) to 16%TS, or higher.
IMPACT OF SLUDGE CONDITIONING ON MECHANICAL DEWATERING AND CONVECTIVE DRYING
Management of sludge produced within wastewater treatment plants has become a key issue. After thickening, the removal of remaining water using mechanical dewatering and/or thermal drying is essential before any type of valorization. Polymers are usually employed in the conditioning step in order to promote particle aggregation, making the dewatering easier. In this work the impact of the polymer dosage and nature on dewatering and convective drying of sludge is studied. Results clearly show the impact of conditioning on dewatering performances, however no effect on drying has been observed within the range of tested experimental conditions.
Quantitative Comparison of Wastewater Treatment Sludge Dewaterability – A Case Study
Increasingly stringent regulations on sludge disposal have heightened the need to understand sludge dewatering. This case study measured the dewaterability of five Melbourne Water sewage treatment plant sludges to quantitatively assess causes of poor filtration. The process involved lab-scale filtration tests and characterisation of dewatering behaviour using a compressive rheology approach. This approach was validated by prediction of the filtration behaviour of the sludges. Sludge dewaterability was quantified using a plate-and-frame filter press model under a standard set of conditions. The results indicate the choice of wastewater treatment process significantly impacts sludge filterability. Specifically, improved dewaterability correlates with extent of digestion and inversely with volatile solids.
Comparison of dewatering characteristics of chemically conditioned
2018
The objective of this study was to compare dewatering properties of chemically conditioned sludge and freeze/thawed sludge as determined by mainly specific resistance to filtration (SRF), dry solids content of sludge cake (DS), and capillary suction time (CST) parameters. The experimental studies were carried out with mixed sludge samples taken from a municipal wastewater treatment plant in Turkey. In chemical conditioning experiments, sludge samples were conditioned with different dosages of polymer using classical jar test method. In freeze/thaw conditioning experiments, samples were frozen at-16.5 °C at different freezing rates and then thawed at 21±1 °C at different times in order to determine the effect of thawing time on dewatering performance. 25 mg/L polymer dose and 2.71 mm/h freezing rate were found to be optimum in terms of sludge conditioning. Rapid freezing that is higher than 8.13 mm/h could not sufficiently condition the sludge and there was no significant effect of thawing time on conditioning performance. Dewatering properties of chemically conditioned sludge and freeze/thawed sludge was determined as very close to each other. While CST and SRF reductions were calculated as 76% and 75%, respectively at 25 mg/L polymer dosage, 2.71 mm/h freezing rate application caused 79% and 76% reduction in CST and SRF, respectively.