Solids Removal Efficiency Research Articles

Sustainable power production from petrochemical industrial effluent using dual chambered microbial fuel cell

Dual chambered microbial fuel cell (DMFC) is an advanced and effective treatment technology in wastewater treatment. The current work has made an effort to treat petrochemical industrial wastewater (PWW) as a DMFC substrate for power generation and organic substance removal. Investigating the impact of organic load (OL) on organic reduction and electricity generation is the main objective of this study. At the OL of 1.5 g COD/L, the highest total chemical oxygen demand (TCOD) removal efficiency of 88%, soluble oxygen demand (SCOD) removal efficiency of 80% and total suspended solids (TSS) removal efficiency of 71% were seen, respectively. In the same optimum condition of 1.5 g COD/L, the highest current and power density of about 270 mW/m2 and 376 mA/m2 were also observed. According to the results of this study, using high-strength organic wastewater in DMFC can assist in addressing the issue of the petrochemical industries and minimize the energy demand.

Removal of fine solids from bitumen by hetero-aggregation and magnetic separation using surface-modified magnetite nanoparticles. Part 2: Role of surface modification

Stearylamine acetate (SAA) modified magnetite nanoparticles (MNPs) have been previously proven to significantly improve the efficiency of fine solids removal from cyclohexane-diluted non-aqueous extracted (NAE) bitumen following magnetic separation. In this work, asphaltene-modified magnetite nanoparticles (Asp-MNPs) were prepared, and their ability to remove fine solids from NAE bitumen was evaluated. The influence of the surface modification with SAA or asphaltene on MNPs in their interactions with NAE fine solids was studied through quartz crystal microbalance with dissipation monitoring and atomic force microscopy studies. It was demonstrated that modification by SAA increased the adhesion interaction between the MNPs and NAE fine solids through a bridging effect. The use of an external magnetic field also strengthened the hetero-aggregation between surface-modified MNPs and the NAE fine solids. Though the asphaltene modification of MNPs resulted in a repulsive behavior in the interaction between MNPs and NAE fine solids due to steric effect, the applied external magnetic field could drive the Asp-MNPs together and induce the bridging among the Asp-MNPs through an interdigitation process, and the NAE fine solids could be captured through a sweeping effect by the networked Asp-MNPs.

Performance analysis of three pilot-scale multi-compartment anaerobic baffled reactors treating domestic wastewater at psychrophilic temperatures in Colorado.

A transition from inefficient aerobic wastewater treatment methods to sustainable approaches is needed. Anaerobic bioreactors are a viable solution as they consume less energy, reduce biosolid production, and provide a source of renewable methane-rich biogas. A barrier to widespread implementation of anaerobic technologies is the lack of design guidance, especially in colder climates. This study bridges this knowledge gap by deriving design principles from three long-running pilot-scale anaerobic baffled reactors (ABRs) operating under psychrophilic conditions. The ABRs removed an average of 56% and 80% chemical oxygen demand (COD) and suspended solids, respectively, with a methane yield of 0.21L CH4 /g CODrem . Methane production may be improved with increased influent sCOD concentrations and decreased sulfate concentrations. Results suggest that ABRs can treat a range of wastewater strengths accompanied by useable methane production. Despite sharing location, temperature, and HRT, the ABRs displayed distinct performances, highlighting the significance of influent wastewater characteristics. PRACTITIONER POINTS: ABRs achieved 56% and 80% removal efficiencies for COD and suspended solids. Average biogas was 63% methane, and methane yield was 0.21 L CH4 /g CODrem . Volumetric methane production was positively correlated with the influent sCOD/sulfate ratio and negatively correlated with influent sulfate loading.

Alternative treatment of olive mill wastewater by combined sulfate radical-based advanced electrocoagulation processes.

The aim of this study is to investigate the performance of advanced electrocoagulation (EC) process for the treatment of olive mill wastewater. In EC process, iron plates were used as electrodes, and peroxydisulfate (PS) and peroxymonosulfate (PMS) were added as oxidants. The effects of the initial pH value, current density, oxidant dose, and electrolysis time were optimized for pollutant removal from olive mill wastewater by EC-PS and EC-PMS processes. Control experiments showed that addition of oxidants to the conventional EC process increased the pollutant removal efficiency. Classical optimization method was used to determine optimum conditions, which were initial pH4, current density 40 mA/cm2 , oxidant dose 5g/L, and electrolysis time 30 min for both processes. Under these conditions, EC-PS and EC-PMS processes achieved 50.5% and 48.9% chemical oxygen demand (COD), 93.8% and 89.3% total phenol, 87.7% and 83% UV254 , and 74.5% and 64.1% total suspended solid removal efficiencies. Quenching experiments were performed to determine the dominant radical species participating in the processes. It was observed that hydroxyl and sulfate radicals were involved in both processes but hydroxyl radicals were more active. Specific energy consumption was calculated as 5.90 kWh/kg COD for EC process, 4.95 kWh/kg COD for EC-PS process, and 5.20 kWh/kg COD for EC-PMS process. The organic removal/sludge ratio of EC-PS process was found to be higher with 17.5g/L value. Although the application of EC-PS and EC-PMS processes alone is insufficient to meet the discharge limits, they have been found to be effective in olive mill wastewater treatment. PRACTITIONER POINTS: Peroxydisulfate (PS) and peroxymonosulfate (PMS)-based advanced electrocoagulation (EC) was used in olive mill wastewater treatment. 50.5% chemical oxygen demand (COD), 93.8% TP, 87.7% UV254 , and 74.5% TSS removals were achieved by EC-PS. 48.9% COD, 89.3% TP, 83% UV254 , and 64.1% TSS removals were obtained by EC-PMS. Hydroxyl and sulfate radicals were involved in both processes.

Investigation of lysing excess sludge slurry using hydrolase secreting thermophilic bacterial communities

Sludge reduction is a critical challenge in biological wastewater treatment. Combining excess sludge slurry lysis technology with traditional activated sludge processes is a promising approach for in-situ sludge reduction. Here, a strategy for excess sludge slurry lysis based on thermophilic bacterial communities (LTBC) was proposed. This investigation focused on the process of excess sludge slurry lysis dominated by thermophilic bacterial communities domesticated at different temperatures (55–75 °C). The evolution of sludge lysate was analyzed, and the mechanism of excess sludge slurry lysis under the action of thermophilic bacterial communities was elucidated through amplicon sequencing analysis. The results demonstrated that the aerobic thermophilic bacterial communities adapted to 75 °C exhibit the highest efficiency in sludge slurry lysis. During LTBC process, the removal efficiency of volatile suspended solids reached 53.9 ± 1.8% within 2 h, and 97.0 ± 1.0% of the protein and 96.0 ± 1.0% of the polysaccharide in the extracellular polymers was solubilized, and bacterial cell walls in sludge were disrupted. Fourier transform infrared spectroscopy and excitation-emission matrix spectroscopy of the sludge lysate demonstrated that the LTBC process was accompanied by humification process. The accumulation of humic acid primarily occurred at 55 °C and 65 °C, while fulvic acid occurred at 75 °C. The thermophilic bacterial communities adapted to 75 °C were dominated by Thermus and Thermaerobacter. Phylogenetic studies showed that the LTBC hydrolase system comprises enzymes related to protein hydrolysis, carbohydrate hydrolysis, and peptidoglycan hydrolysis, including metalopeptidase MepB, neutral α-glucosidase C, N-acetyl Muramyl-L-alanine amidase, and others enzymes. These results provide a theoretical basis for the application of LTBC technology in the reduction of sludge which generated in traditional waste water activated sludge processes.

Sludge lysis by thermophilic bacteria community enhances nutrient removal, sludge reduction, and modulates microbial community in anaerobic-anoxic-oxic process

Excess sludge generated during the biological treatment of wastewater is returned to the biochemical tank after being lysed, which is considered to be a feasible strategy for reducing sludge. In this study, an in-situ sludge reduction technology combining sludge lysed based on thermophilic bacterial community (LTBC) and anaerobic-anoxic-oxic (AAO) process (i.e., LTBC-AAO process) was proposed for the first time and the sludge reduction efficiency of the LTBC-AAO process was evaluated. In LTBC reactor, the average removal efficiency of volatile suspended solids of sludge was 52.1 ± 3.2 %. Thermophilic bacteria involved in sludge lysis included Thermus, Fervidobacterium and Caldanaerobacter with relative abundances of 51.5 %, 20.3 % and 8.72 %, respectively. The excess sludge of LTBC-AAO was reduced by 64.7 % compared with that of conventional AAO. The COD removal efficiencies of LTBC-AAO and AAO were 93.4 ± 1.8 % and 93.1 ± 2.1 %, respectively, and there was no significant difference. The TN removal efficiency of LTBC-AAO was 65.7 ± 4.2 %, which was 10 % higher than that of AAO (55.7 ± 3.2 %). Furthermore, 65.7 % substrate in lysed sludge supernatant was readily biodegradable, and the denitrification rate of these substrates as carbon source was 6.33 mg N/g VSS-h. Microbial community structure analysis revealed increased microbial diversity of activated sludge due to lysed sludge reflux, with enrichment of denitrification-related species Delftia and Acinetobacter in LTBC-AAO contributing to the improvement in nitrogen removal efficiency. These findings suggest that the LTBC-AAO process is a promising technology for sludge reduction and nutrient removal in municipal wastewater treatment plants.

Effect of varying retention times and feeding schemes on the performance of vertical constructed wetlands planted with vetiver grass in treating dairy wastewater in the Philippines

AbstractAdequate wastewater treatment from the dairy industry before disposal is still lacking in the Philippines, particularly in small‐scale sectors. This limitation is due to the high cost and expertise required from conventional wastewater treatment systems. One option is using constructed wetlands, a nature‐based solution with low cost, less specialized expertise and maintenance requirements and high wastewater treatment efficiency. To further evaluate the application of constructed wetlands in the Philippines, this paper studied the wastewater from the manufacturing processes of the Dairy Training Research Institute, University of the Philippines Los Baños (DTRI‐UPLB). It is a small dairy farm inside the University with economic constraints in using a conventional wastewater treatment system. The main aim of this study is to determine the effect of using vertical subsurface flow constructed wetlands (VSSFCW) planted with Vetiver grass (Chrysopogon zizanioides) in sand and gravel media to treat the DTRI‐UPLB effluent, using very low retention times (4 and 8 h), with daily and alternate days of wastewater feeding into the VSSFCW. The average removal efficiencies for total suspended solids (TSS), biological oxygen demand for (BOD5), total phosphorus (TP), and Total Kjeldahl Nitrogen (TKN) are 88.34%, 93.56%, 78.42%, and 94.63%, respectively. Moreover, alternate wastewater feeding provided a statistically significant increase in the performance of VSSFCW, while there is no statistical difference between the two retention times evaluated. Finally, it was observed that plant age significantly affects the performance of VSSFCW setup but should be explored further with longer operation times and additional nutrient uptake analysis.

Prediction on Filtration Period of Granular Bed Filter Used in Purifying Produced Water in Oil Field

Summary The granular bed filter can purify the water produced in the crude oil production process by adsorbing oil droplets and suspended solids. A regeneration operation is needed to clean the granular media and recover filtration capacity after a certain operation duration. Currently, filtration models are mainly used for one type of particle removal, with few applications in the filtration system of produced water containing oil droplets and suspended solids. However, the different deposition morphologies of oil droplets and suspended solids in the filter bed can affect the prediction of the filtration process. In this work, we develop a transient filtration model based on the multiphase system transport equations coupled with the filtration rate and momentum exchange equations to predict simultaneously the effluent concentration and the pressure drop buildup, which considers the effect of deposition morphologies of oil droplets and suspended solids on filtration behaviors. The model hypothesizes that particle removal occurs through deep bed filtration mechanisms, and initial filtration coefficients are predicted by trajectory analysis without relying on experimental data. After that, we propose a method for predicting the filtration period, and analyze the effect of particle size and water temperature on the filtration process. Results show that the filtration process can be divided into two major stages—the main filtration zone migration, followed by the saturation front migration. With an S-shape increase in the effluent concentration, the pressure drop of the filter bed increases in a parabolic shape. When the diameter median of suspended solids is 5 μm, and the water temperature is 20°C, the filtration period was determined to be 24 hours to meet both water quality and maximum usable pressure drop of 20 kPa. With the increase in non-Brownian suspended solid size, the interception and gravitational forces increase the removal efficiency of suspended solids, which results in a slight decrease in the removal efficiency of oil droplets and an increase in the pressure drop of the filter bed. As the water temperature increases, the viscosity of the produced water decreases, and the oil droplets and suspended solids are more easily removed, but the pressure drop of the filter bed increases. In this work, we provide new ideas and methods to properly design, operate, and manage filters in a sustainable and energy-efficient way.

Ultrafiltration of digestate liquid fraction by hollow-fiber membranes: Influence of digestate pre-treatment on hydraulic capacity and nutrient removal efficiency

With the growing interest in anaerobic digestion as a processing method of agro-food waste, proper disposal of digestate has become a prominent problem. In the study, ultrafiltration of the sugar beet pulp digestate was conducted using hollow-fiber membranes with a cut-off of 150 kDa operating in an outside-in system. The effect of different pre-treatment strategies of digestate i.e. centrifugation alone or in combination with coagulation with polyaluminium chloride, biocoagulation with chitosan and flocculation with polyacrylamide on mitigation of membrane fouling and permeate quality was investigated. High ultrafiltration performance was obtained using centrifugation followed by flocculation with 416 mg/dm3 of polyacrylamide as digestate pre-treatment. Removal efficiencies of chemical oxygen demand (COD), total solids, phosphorus and nitrogen were 89.80, 90.08, 88.37 and 64.12%, respectively. Permeate flux and total membrane resistance averaged 22.33 dm3/m2/h and 5.32 • 1011 m−1. Hydraulic parameters and removal rates determined during ultrafiltration preceded by centrifugation and biocoagulation with 100 mg/dm3 of chitosan did not differ significantly from the values mentioned above for the pre-treatment consisting of centrifugation and flocculation with polyacrylamide. The results indicate the possibility of filtering the liquid fraction obtained by centrifugation, coagulation or flocculation of the digestate, and using natural auxiliary agents during its pre-treatment.

Biogas production from food waste hydrolysate using a subcritical water pretreated process and pulp wastewater seed sludge

This study was investigated the biogas production performance from subcritical water hydrolysate (SCWH) using a pretreated food waste (FW) process, and pulp wastewater (PW) as seed sludge according to different volatile solid (VS) ratio of PW to SCWH, and different substrate concentration. The subcritical water hydrolysis was acted for 30 mins in a 70 ml Teflon reactor under different temperatures varied from 119, 129, 139, 159, and 195 ℃, respectively. A batch system for optimal biogas and methane production yields examination were fermented in a 60 ml flask under 37 °C and 120 rpm. A maximum biogas yield of 807.0 ml/g VSre and methane yield of 329.5 ml/g VSre were achieved at a VS ratio of PW to SCWH 1:3 and substrate concentration of 25 g/L with a hydrolysate under 159 ℃ and the volatile solids (VS) removal efficiency of 80%. These results indicated that the food waste pretreated by subcritical water hydrolysis can efficiently increase the biogas production under optimal conditions.

Side-stream membrane-based NH3 extraction to improve the anaerobic digestion of poultry manure

The influence of membrane-based ammonia extraction on poultry manure (PM) wastewater treatment was assessed in a 3 L continuous stirred tank reactor (CSTR). The anaerobic digester operated for 91 days at a hydraulic retention time of 15 days and 37 °C. The flat sheet polytetrafluoroethylene (PTFE) membrane module was interconnected to the CSTR and operated at a recirculation flow rate of 0.25 L min−1. The membrane-based ammonia extraction mediated a decrease of total ammonia nitrogen of 64.5 % and of total nitrogen of 53.4 %, which induced an increase in the methane yields from 360 ± 70 up to 574 ± 5 N mL CH4 g VS fed−1. Similarly, chemical oxygen demand (COD) and volatile solids (VS) removal efficiencies increased from 59 % ± 2 % and 57 % ± 3 % up to 79.1 % ± 0.8 % and 65.8 % ± 0.2 %, respectively. This work targeted the enhancement of the performance of full-scale anaerobic digestion plants via reduction of NH3 concentration with a membrane-based extraction unit.

An Experimental Study on optimizing Wastewater Filtration through Conventional and Capped Rapid Sand Filter

Abstract: Rapid sand filtration is a widely adopted technique for purifying water in various applications, ranging from municipal water treatment plants to industrial processes. This abstract provides an overview of the rapid sand filter, highlighting its key principles, advantages, and applications. The rapid sand filter is a gravity-driven filtration system that utilizes a bed of sand as the primary filtration medium. Water flows through the sand bed under gravity or low-pressure conditions, undergoing physical andbiological processes that remove suspended solids,pathogens, and other impurities. The sand bed acts as a physical barrier, trapping and retaining particles while allowing the passage of clean water. This abstract discusses the key factors influencing the efficiency of rapid sand filters, including sand grain size, uniformity, and depth. The control of filtration rate, backwashing frequency, and the use of coagulants or flocculants are also addressed, as they significantly impact the filter's performance. Proper maintenance and monitoring are crucial to ensure optimal filter operation and prevent clogging or biofilm formation. Rapid sand filtration offers several advantages, such as simplicity, cost-effectiveness, and ease of operation. It is capable of achieving high removal efficiencies for suspended solids, turbidity, and certain pathogens, making itsuitable for a wide range of water treatment applications

Automatic Flushing Strainer-Type Filter: A Method for Actual Filtration Grade Assessment

Proper filtration selection, sizing, maintenance, and performance of a filtration system are crucial for removing suspended solids in water, preventing clogging of emitters, and ensuring a high-performing microirrigation system throughout its lifespan. Filtration prevents the intake of particles larger than the pore size specified in a given filtration grade. Proper selection of the filter media ensures efficient solid–liquid separation. Strainer-type or screen filters have elements composed of a woven or nonwoven cloth of numerous weave types. The material and characteristics of the screen directly affect the fluid flow and filter performance. The aim of this study is to propose a method for determining the actual filtration grade of filters used for irrigation. An automatic flushing strainer-type filter was equipped with five filter element models, composed of woven and nonwoven materials, for evaluation. A new methodology was developed to assess the actual filtration grade based on the removal efficiency for suspended solids under controlled and repeatable conditions. The removal efficiency of each filter element was determined for particle size ranges defined according to the filtration grade declared by the manufacturer. The proposed methodology allowed for the assessment of the actual filtration grade of each model of filter element operated with water containing suspended particles of silica sand. The filtration grade declared by the manufacturer was confirmed for some of the filter elements, but it could be modified for others. The proposed methodology could be useful for assessing the actual filtration grades of screen, disk, and media filters.

Improving secondary settling tanks performance by applying CFD models for design and operation

Abstract This study uses computational fluid dynamics (CFD) models for an improved performance of secondary settling tanks, taking as a case study the wastewater treatment plant (WWTP) of Souk-Ahras City, Northeastern Algeria. Unlike previous studies, which focused primarily on simulations of real-time clarifiers by independent measures, this study combines differentoperating criteria and geometric standards on clarifiers to estimate the ultimate capacity of secondary sedimentation tanks (SST). Numerical simulations were performed toassess the SST hydraulic performance under different conditions in order to (i) eliminate vortex zones; (ii) optimize the surface overflow rate (SOR) and predict sludge blanket height (SBH), and finally, (iii) estimate SST ultimate capacity. Based on the current configuration of the SST of Souk-Ahras WWTP, its hydraulic treatment capacity was found to be 49,000 m3/d. The results obtained, which were validated by field observations, showed that optimizing the different parameters yields a significantly improved SST performance. Furthermore, the tests consideredwere shown to be satisfactorily correlated with SOR. Validation using the receiver operating characteristic (ROC) curve analysis yielded anarea under curve (AUC) value of 90%, implying thereby a reasonably good performance. Indeed, optimization resulted in increased solidremoval efficiency and increased SOR to 1.4 m.h−1 (compared to 0.8 m.h−1 in literature) without overflow beyond the SBH.

Bioaugmentation with Bacillus subtilis and Cellulomonas fimi to enhance the biodegradation of complex carbohydrates in MFC-fed fruit waste

The present study aimed to investigate the biodegradation of waste fruit by microbial fuel cells (MFC) when employing bioaugmentation of polysaccharides degrading bacterial strains and in-situ produced fungal mash. Bioaugmentation with Cellulomonas fimi and Bacillus subtilis both separately and in combination resulted in high chemical oxygen demand removal, high carbohydrates removal, and high solids removal efficiency, which is a slow process otherwise. The results revealed that Cellulomonas fimi alone achieved 60% and 17% higher chemical oxygen demand removal in 24 and 48 h respectively, than control treatment sludge. Cellulomonas fimi alone and in combination with Bacillus subtilis displayed an efficient carbohydrates removal of >90%. Fungal pre-treatment filtered also displayed high organics removal, the coulombic efficiency, however, remained 144% lower than Cellulomonas fimi and Bacillus subtilis augmented reactor. The presented results demonstrate that microbes are crucial for effective functioning of MFC, and high organics removal can be achieved with the use of right microbial cultures.

Evaluation of Ti/Pt Anode Efficiency and Energy Consumption in Turbidity and Suspended Solids Removal from Paper Industry Wastewater: The Effect of pH and Support Electrolyte Type

In the research, different experimental setups were used to examine the treatment of wastewater from the paper industry using the electrooxidation method, one of the electrochemical treatment methods in the batch system. In the 2000 mL volume jacketed glass reactor utilized for the treatment of wastewater from the paper industry, 4 anode and 4 cathode sieve type plates of 7 cm x 10 cm dimensions were positioned at 0.5 cm intervals, and 1200 mL wastewater was used in the tests. Coated sieve type Ti/Pt electrodes were employed as the anode in the electrooxidation studies, and uncoated sieve type Ti electrodes were used as the cathode. It was determined that the active anodic wet surface area was 1078 cm2 . The removal rates of pollutant parameters such as turbidity and SS (Suspended Solids) in the experiments; the effects of wastewater initial pH value and supporting electrolyte type parameters were investigated. According to the results, the most effective pH value for Ti/Pt anode type at 400 rpm mixing speed was determined to be waste water natural pH (7.5), and 0.50 M NaCl was the most successful supporting electrolyte type. 96.92% Suspended Solids removal efficiency and 95.38% turbidity removal efficiency for Ti/Pt anode were achieved under ideal conditions. In addition, 312.05 kW-hour/kg COD is determined as the energy consumption value.

Constructed wetland technology for the treatment and reuse of urban household greywater under conditions of Africa's Sahel region

Abstract Three pilot systems of a constructed wetland were assessed to advance the urban reuse of greywater for household gardening in areas of the world representative of Africa's Sahel (one unplanted and two planted with local species, namely Andropogon gayanus and Chrysopogon zizanioides). Principal component analysis showed planted systems provided higher removal efficiencies than the unplanted system and A. gayanus performed better for treating most water quality parameters. As expected, removal efficiencies for suspended solids (SS) and chemical oxygen demand (COD) were greater than 90% in all filters. The removal of five-day biochemical oxygen demand (BOD5) was, however, significantly greater in the filter planted with A. gayanus than in the unplanted control. For plant-beneficial parameters such as nutrients (NO3−, NO2−, NH4+, and PO43−), the removal in the planted filters was significantly higher than in the unplanted filter (>90% versus 73%–78%). The reduction of fecal coliforms was significantly greater in the two planted systems and exceeded 2.5 log10 removal. Analysis of the microbial water quality characteristics showed the concentration of fecal microbial indicators would achieve WHO guidelines for restricted irrigation with retention of some embedded nutrients, thus reducing pressures on areas experiencing climate variability, water scarcity, and land degradation.

Suspended solid removal efficiency of plate settlers and tube settlers analysed by CFD modelling.

Removal of suspended solids from raw water is an essential process in water treatment plants. Conventional sedimentation tanks in water treatment plants occupy a large area and become expensive in urban areas. The use of plate settlers or tube settlers in sedimentation tanks to increase the efficiency and hence reduce the footprint of sedimentation tanks is an economical solution in water treatment. This study investigated the effectiveness of plate and tube settlers compared to conventional settlers in a water treatment plant. A three-dimensional Computational Fluid Dynamics (CFD) model was set up using ANSYS-CFX 17.2. Seven cases (a conventional settler, three plate settlers and three tube settlers) were analysed to compare the settler performances. The maximum removal efficiencies of all solid classes were approximately equal in plate and tube settlers with the same plate spacing and tube depth: around 100%, 67%, 28% and 9% for the solid classes with particle diameters of 41, 17, 9.5 and 5.0 µm, respectively. The settling efficiency remained unchanged with the increase of the plate settling area beyond 60% of the conventional settler area under the given tank and flow conditions. The tube cross-section shape does not affect the particle removal efficiency of a tube settler.

Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m−3.d−1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10–0.05 m3.kgTVSfed−1.d−1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 106 MPN.g TVS−1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

Bioproducts from anaerobic co-digestion of organic fraction of municipal solid waste: substrate mixing ratios for power, heat and digestate potential assessment as support for scale-up

Thisresearch investigated the use offood waste - FW and garden waste - GWas substrates for producing thermic and electric energy on a labbioreactor. A mesophilic continuous stirred-tank reactor (CSTR) was used to support the operational planning of a pilot-scale Plant, consisting indigesters of 430 m3. The bioreactor was operated during 284 days under organic loading ratesfrom1.4 to 3.9 kg VS/m3. d and using different FW:GW ratios to simulate cities routine. The operation of the CSTR showed pH stability, high efficiency of solids removal (74.8 to 97.3%), and a maximum methane yield of 0.51 L CH4/gVS. Considering the most efficient scenario, it was calculated an electric and thermic energy potential of 183 kWheand 554 kWhtper ton of fresh matter. Regarding to the energy yield, up to 18.5 kJ/g VS was estimated. The composite sample of the digestate revealed nitrogen, sodium and potassium as major compounds (1530, 1350, and 1300 mg/L, respectively),and heavy metals under safe limits.As future scope, the presented energy simulations through metane-based energy production system may serve as a boosting step for Biogas Plants, providing valuable references for real scale applications from different proportions of organic urban residues.