Tank Sludge Research Articles

Towards a CFD-based analysis of a full-scale sludge tank to enhance dewatering capacity of the downstream filter press

Abstract A computational fluid dynamics (CFD) model was developed for sludge mixing-settling in a laboratory scale sludge tank based on the Takacs exponential function. A dynamic experimental program was also undertaken at different rotational speeds of mixers and the concentration of sludge to validate the sludge sump model. The deviation between the simulated interface height and the experimental data was 2%. The validated CFD model was then employed to develop a novel operating methodology for operation of a full-scale sludge tank. The proposed model includes two consecutive periods of sludge mixing and settling, resulting in reducing the mixers’ working time. In the current operating mode, the energy consumption of mixers has been reduced by 91.67%. Based on the two-phase, 3-D modeling results of the sludge tank, the post-construction sludge tank is simultaneously able to act as a secondary clarifier, as well as a storage tank. As a key finding of the study, the treatment capacity of the filter press in downstream has accelerated, so that the working hours and energy consumption of the filter press has been improved by 55%.

Numerical simulation and optimization of cleaning bidirectional nozzle of large petroleum storage tank

In the process of storing petroleum for a long time, the coagulability substance in the petroleum will form high viscosity petroleum sludge at the bottom of the tank, resulting in the loss of petroleum, the decrease of reserves, and the internal corrosion. The main components of petroleum sludge are petroleum and wax, which have certain recycling value. In this paper, the numerical simulation technology is used to simulate and optimize the flow field of the bidirectional nozzle in the large petroleum tank cleaning device. The shape of the nozzle with fast velocity, steady jet-flow and high efficiency, solves the problem of deposit and cleaning of petroleum sludge in petroleum tank, and provides a new idea for the future design of the mechanical cleaning device for the petroleum tank.

Sustainable microalgae cultivation by using anaerobic centrate and biogas from anaerobic digestion

This research was conducted to determine the effectiveness of using biogas generated from the anaerobic digestion of septic tank sludge and its anaerobic centrate on microalgal cultivation. Three types of sparging gas (biogas, air, and nitrogen gas) and two culture media (anaerobic centrate and Bold Basal Medium) were used to generate six different experimental settings. The most microalgal growth of 1074 mg VSS/L was achieved when both biogas and anaerobic centrate were used after 10 days of cultivation at 30 °C. In addition, the anaerobic centrate used had a reduction of 89% in its soluble chemical oxygen demand, a 97.3% reduction in the phosphorus concentration, and a 71.5% reduction in the nitrogen concentration. The results demonstrated tremendous benefits of biogas reuse and anaerobic centrate reclamation via microalgae cultivation.

Methanogenic biodegradation of crude oil storage tank sludge enhances bio-corrosion of mild steel

Methanogenic biodegradation of crude oil sludge was investigated using chemical and molecular approaches. 16S rRNA gene sequences recovered from the samples revealed significant presence of Marinobacterium (63%), Pseudomonas (3%), acetotrophic Methanosaeta (16%) and hydrogenotrophic Methanobacterium (5%). The resident microbial community was able to reduce the gravimetric weight of residual oil by 65.5% (with complete degradation of C5–C17 n-alkane fractions) in non-amended samples and 94.13% (with complete degradation of C5–C25 n-alkane fractions) in substrate-amended samples during the 60-day incubation period. As biodegradation progressed, acetotrophs consume acetate at the rate of 0.41 mM/day−1 while hydrogenotrophs consume hydrogen at the rate of 0.59 mM/day−1. Respective volume of methane produced and corrosion rates observed were higher in highly biodegraded samples (3.60 mmol/0.084 mm/year) than lesser biodegraded samples (1.64 mmol/0.018 mm/year). Our results showed that the resident methanogenic archaea were largely responsible for the anaerobic biodegradation of hydrocarbons in crude oil sludge and biodegradation was enhanced with substrate amendment, which further accelerated the corrosion rates of mild steel coupons. Considering the relatively high number of facultatively anaerobic Marinobacterium and significant presence of Pseudomonas in the sequenced data, we speculate that the bacteria were at least partially responsible for biodegradation of crude oil components potentially acting as syntotrophic organisms with methanogens to convert crude oil to methane and subsequently enhance corrosion rates of mild steel coupons.

Co-treatment of septage and municipal wastewater in a quadripartite microbial desalination cell

Most microbial desalination cells (MDCs) in previous research were constructed of three chambers fed with municipal wastewater as anolyte. In the present study, a unique design of MDC, named quadripartite microbial desalination cell (QMDC), was designed and fabricated to demonstrate the feasibility of a 9-chamber MDC for co-treatment of septage (septic tank sludge) and municipal wastewater. It was found that maximum power density, COD removal in anode chamber, and desalination rate at the COD concentration of 4911.6 ± 71 mg L−1 (mixing ratio of 1:10) were 8.16 W m−3, 58.4%, and 72.8% over a short-term operation; corresponding data in QMDC containing lower COD concentration (mixing ratio of 1:100) decreased to 7.2 W m−3, 49.8%, and 69.7%, respectively. In addition, longer operation of QMDCs showed a significant drop in the performance of QMDC fed with higher fraction of septage (mixing ratio of 1:10). Regarding COD removal, transferring treated anolyte solution from anode to cathode chamber improved total COD removal by 91.1%. It was found that although QMDC performance in electricity production and salt removal was relatively better in mixing ratio of 1:10, the use of higher mixing ratio (1:100) is firmly suggested because of higher stability of the process under long-term operation.

CO2 and N2O from water resource recovery facilities: Evaluation of emissions from biological treatment, settling, disinfection, and receiving water body

Water resource recovery facilities (WRRFs) contribute to climate change and air pollution, as they are anthropogenic potential sources of direct and indirect emission of greenhouse gases (GHGs). Studies concerning the monitoring and accounting for GHG emissions from WRRFs are of increasing interest. In this study, the floating hood technique for gas collection was coupled with the off-gas method to monitor and apportion nitrous oxide (N2O) and carbon dioxide (CO2) emissions from both aerated and non-aerated tanks in a municipal water resource recovery facility, in order to investigate its carbon footprint (CFP). To our knowledge, this is the first time that the chamber technique was applied to evaluate gas fluxes from the settler, where an emission factor (EF) of 4.71 ∗ 10−5 kgCO2,eq kgbCOD−1 was found. Interesting results were found in the disinfection unit, which was the major contributor to direct N2O emissions (with a specific emission factor of 0.008 kgCO2,eq kgbCOD−1), due to the chemical interaction between hydroxylamine and the disinfectant agent (hypochlorite). The specific emission factor of the biological aerated tank was 0.00112 kgCO2,eq kgbCOD−1. The average direct CO2 emission was equal to 0.068 kgCO2 kgbCOD−1 from the activated sludge tank and to 0.00017 kgCO2 kgbCOD−1 from the secondary clarifier. Therefore, taking into account the contribution of both direct N2O and CO2 emissions, values of 0.069 kgCO2,eq kgbCOD−1, 0.008 kgCO2,eq kgbCOD−1 and 0.00022 kgCO2,eq kgbCOD−1, were found for the net CFP of the aerated compartment, the disinfection unit and the clarifier, respectively.The plant energy Footprint (eFP) was also evaluated, confirming that the aeration system is the major contributor to energy consumption, as well as to indirect CO2 emission, with a specific eFP of 1.49 kWh kgbCOD−1.

Dewatering of septic tank sludge in alternative sludge drying bed

Abstract In dewatering of septic tank sludge, the sludge drying bed is one of the main techniques used, but it demands a great deal of area and time for the removal of sludge cake. Modification of this system using permeable pavements and polymer can minimize such problems, facilitating the management of sludge when decentralized sanitation is used. Therefore, the objective of this study was to compare the dewatering of septic tank sludge using conventional sludge drying bed (CSDB) and a sludge drying bed with permeable pavement (SDBPP). At the same time of dewatering, the volume drained by the SDBPP was 37.4 ± 4.6% higher than that obtained in the CSDB. Therefore, a lower drying bed could be used. It was found that the use of synthetic polymer allowed dewatering to occur in less time, but did not interfere in the solids content of the sludge cake. The reuse of the pavement was proven possible, but required large volumes of water and mechanical equipment.

Methods to reliably estimate faecal sludge quantities and qualities for the design of treatment technologies and management solutions

Sanitation access in urban areas of low-income countries is provided through unstandardized onsite technologies containing accumulated faecal sludge. The demand for infrastructure to manage faecal sludge is increasing, however, no reliable method exists to estimate total accumulated quantities and qualities (Q&Q) This proposed approach averages out complexities to estimate conditions at a centralized to semi-centralized scale required for management and treatment technology solutions, as opposed to previous approaches evaluating what happens in individual containments. Empirical data, demographic data, and questionnaires were used in Kampala, Uganda to estimate total faecal sludge accumulation in the city, resulting in 270 L/cap∙year for pit latrines and 280 L/cap∙year for septic tanks. Septic tank sludge was more dilute than pit latrine sludge, however, public toilet was not a distinguishing factor. Non-household sources of sludge represent a significant fraction of the total and have different characteristics than household-level sludge. Income level, water connection, black water only, solid waste, number of users, containment volume, emptying frequency, and truck size were predictors of sludge quality. Empirical relationships such as a COD:TS of 1.09 ± 0.56 could be used for more resource efficient sampling campaigns. Based on this approach, spatially available demographic, technical and environmental (SPA-DET) data and statistical relationships between parameters could be used to predict Q&Q of faecal sludge.

Modeling temperature effects in anaerobic digestion of domestic wastewater

A combination of septic tank (ST) and up-flow anaerobic sludge blanket (UASB) as treatment for domestic wastewater was modeled with the anaerobic digestion model 1 (ADM1). The model was used to visualize the influence of temperature and organic load. The UASB process alone and the combined ST-UASB were simulated with temperature compensation kinetics for low temperature conditions 10, 15 and 20 °C. The combination of ST and UASB reactor allowed high and predictable overall COD removal even at low temperatures and high organic loads. This model underestimates COD accumulation and COD removal, while overestimating biogas production by up to 15%. However, the UASB model applied is quite reasonable in predicting the behavior of such a process in estimating biogas production and COD removal of domestic wastewater pretreated by a ST. The modeling approach presented can become a useful tool to evaluate and design low cost ST-UASB systems for fluctuating climatic environment such as Nepal.

Bioaugmentation strategy for the treatment of fungicide wastewater by two triazole-degrading strains

In this study, bioaugmentation potential of 1H-1,2,4-triazole (TZ) degrading strain namely Shinella sp. NJUST26 and tricyclazole (TC) degrading strain namely Sphingomonas sp. NJUST37 was evaluated in a bench-scale activated sludge tank. The performance of the bioreactor demonstrated the feasibility of bioaugmentation by NJUST26 and NJUST37 in terms of almost complete TC and TZ removal, significant COD and TOC removal, as well as toxicity reduction. The effect of influent pH, hydraulic retention time (HRT) and triazole fungicide concentration was investigated in order to reach an optimal treatment performance. The bioaugmented process after the inoculation of NJUST26 and NJUST37 could maintain stable performance in terms of TZ, TC, COD and TOC removal from the wastewater. High-throughput sequencing analysis suggested that higher diversity and significant shifts in bacterial community structure were achieved after the inoculation of NJUST26 and NJUST37. However, both NJUST26 and NJUST37 lost their dominance during long-term operation, despite of the key role of the inoculation of NJUST26 and NJUST37 in the formation of effective microbial community.

Direct dosage of reactivated carbon from waterworks into the activated sludge tank for removal of organic micropollutants.

The thermal reactivation of granular activated carbon is a substantial ecological and economic benefit in the process of drinking water treatment. A significant amount of abraded carbon, which is similar to powdered activated carbon (PAC), is produced that can be brought to application at wastewater treatment plant level for the removal of micropollutants in a powdered activated carbon-activated sludge (PAC-AS) system. This excess carbon derived as a by-product from the reactivation process in a waterworks was applied directly into the activated sludge tank and has been elevated in this study by monitoring the removal efficiencies for benzotriazole, carbamazepine, diclofenac, metoprolol and sulfamethoxazole in the effluent of a semi-technical wastewater treatment plant of 39 m3. A simulation-derived sampling strategy was applied to optimize the recovery rates of the micropollutants. Flow-proportional, 72-hour composite sampling was considered best. The elimination rates obtained for a 10 g PAC·m-3 dosage were 73% for benzotriazole, 59% for carbamazepine, 60% for diclofenac, 67% for metoprolol and 48% for sulfamethoxazole. The obtained results underline the importance of appropriate sampling strategies, which can be derived from hydraulic modeling.

A pilot-scale study on a down-flow hanging sponge reactor for septic tank sludge treatment

A pilot-scale study on a down-flow hanging sponge reactor for septic tank sludge treatment

DEVELOPMENT OF A COMPUTER PROGRAMME FOR THE DESIGN OF MUNICIPAL WASTEWATER TREATMENT FACILITIES Part 6: Sludge Thickening and Blending Facility

The first sludge proc essing unit in a municipal wastewater treatment plant is sludge blending tank and sludge thickener before the sludge flow into sludge stabilization unit. A computer programme was developed using FORTRAN to design sludge blendin g tank and sludge thickening facility. The design include determining the size and hydraulic profile in the sludge thickener and in sludge blending tank. The influent and effluent structure is also designed using the same method in the secondary clarifier. The' input data to this computer programme is mainly the quantity of sludge effluent from the primary sedimentation bas ins and from the secondary or final clarifiers. These values are computed in a separate subroutine which analyze the material mass balance in the treatment plant. The thickened sludge withdrawal rate and the effluent quality from the sludge thickener are also computed . The results are easy to interpret and automatically appear on the computer screen or in an output file.

Concentration of active sludge in the aeration reactors

The purpose of the paper was to study the dehydrogenase activity (DHA) of activated sludge in aeration tank. The article describes a change in enzyme activity, (dehydrogenase activity of sludge-DHA) of activated sludge while various time of aeration as well as various dose in sludge of aeration tank. Assessment changes enzyme activity were done on two indicators - on DHAor. (original dehydrogenase activity of sludge) and DHAH2O (dehydrogenase sludge activity with tap water). In the first case - DHA with the actual substrate, in the second case - DHA with poorly concentrated substrate. The work was performed on a pilot installation consisting of four models of aeration tanks blocked with sedimentation tanks, on a real city waste water. Working doses of sludge in biological wastewater treatment process was ranged from 2 to 6 g/l, time of aeration in aeration tanks changed from 3.5. up to 0.8 hours. Experimental studies have shown that regardless of the size of working sludge dose in aeration tank character of changes DHA or and DHAH2O is identical.

Fractal analysis of biological wastewater treatment efficiency

The purpose of the present research was to enhance the efficiency of biological wastewater treatment through the direct impact on the metabolism of activated sludge. In the course of research, species and quantitative composition of biological community of activated sludge in aeration tanks during wastewater purification process was studied. Comparative analysis was carried out for linen production wastewater and household sewage. Possible application of biological treatment in linen production was evaluated. Proposals were developed on creation of controllable biological treatment facility. In this paper, biological methods are shown to be efficient for household sewage treatment. Comparative analysis was carried out for linen production wastewater and household sewage. Possible application of biological treatment in linen production was evaluated. Proposals were developed on creation of controllable biological treatment facility.

The diversity of microorganisms inhabiting the sludge tanks of Baikalsk pulp and paper plant (BPPP)

The wastes from the Baikalsk pulp and paper plant, including the by-products of the plant’s bleaching unit are stored in the special disposal reservoirs in the form of a sludge-lignin, which consists of lignin, polyacrylamide and flocculants. Here, we report on microbiological composition of sludge-lignin: we detected fungi hyphae, actinomycete hyphae, long and short rods as well as coccal forms of bacteria. Interestingly, despite the diversity of bacterial, cyanobacterial and fungal communities no noticeable destruction of lignin was observed. We recommend to use specific chemical compounds and microbiological agents for destruction of sludge-lignin.

Discharge quality from municipal wastewater treatment plants and the Sludge Biotic Index for activated sludge: integrative assessment

Abstract Wastewater treatment plants (WWTPs) are scrutinized by Environmental Authorities particularly regarding the compliance to discharge limit values fixed by national and local regulations. An integrated approach is necessary to achieve the objectives established with Directive 2000/60/EC (WFD) considering the ecological status of the receiving water body and the quality of the discharge. Specifically, documentary, technical, management and analytical controls should be developed. Moreover, integrative information on the behaviour of the activated sludge in the aeration tank can be useful for plant managers as well as for the regulating Authorities. The study presents the experience concerning WWTP regulation considering the analytic assessment of the discharge as well the monitoring of the Sludge Biotic Index (SBI) for activated sludge. Data from monitoring during the period 2008–14 on SBI values and chemical and microbiological data on the discharges of a sample of 35 WWTPs in the province of Venice (north-east Italy, Veneto region) are presented and discussed. Together with chemical and microbiological analysis, the SBI appears to be a highly useful index for the integrative assessment of plant functionality, in particular when monitoring and identifying critical situations that can determine the exceedance of discharge limit values. The SBI method, in an integrated control approach, can be used for small and medium sized WWTPs that only treat domestic wastewaters. In a case by case assessment this may even substitute part of the analytical monitoring carried out in the WWTPs' control process.

Multi-point monitoring of nitrous oxide emissions in three full-scale conventional activated sludge tanks in Europe.

The large global warming potential of nitrous oxide (N2O) is currently of general concern for the water industry, especially in view of a new regulatory framework concerning the carbon footprint of water resource recovery facilities (WRRFs). N2O can be generated through different biological pathways and from different treatment steps of a WRRF. The use of generic emission factors (EF) for quantifying the emissions of WRRFs is discouraged. This is due to the number of different factors that can affect how much, when and where N2O is emitted from WRRFs. The spatial and temporal variability of three WRRFs in Europe using comparable technologies is presented. An economically feasible and user-friendly method for accounting for the contribution of anoxic zones via direct gas emission measurements was proven. The investigation provided new insights into the contribution from the anoxic zones versus the aerobic zones of biological WRRF tanks and proved the unsuitability of the use of a single EF for the three WRRFs. Dedicated campaigns for N2O emissions assessment are to be advised. However, similarities in the EF magnitude can be found considering treatment strategy and influent water composition.

Performance of mortars with the addition of septic tank sludge ash

This paper studies the performance of mortars with the addition of septic tank sludge ash (SA). The sludge is a non-dangerous and non-inert residue. The cement-sand content is 1:3, in mass, commonly used for masonry in building construction. The percentages of sludge ash additions were 5, 10, 15, 20, 25 and 30% related to the cement mass. The results show that the addition of SA improves the general condition of the mortars, within the limits studied in this paper, providing better performance on both fresh and hardened states.

Energy consumption of agitators in activated sludge tanks – actual state and optimization potential

Depending on design capacity, agitators consume about 5 to 20% of the total energy consumption of a wastewater treatment plant. Based on inhabitant-specific energy consumption (kWh PE120-1 a-1; PE120 is population equivalent, assuming 120 g chemical oxygen demand per PE per day), power density (W m-3) and volume-specific energy consumption (Wh m-3 d-1) as evaluation indicators, this paper provides a sound contribution to understanding energy consumption and energy optimization potentials of agitators. Basically, there are two ways to optimize agitator operation: the reduction of the power density and the reduction of the daily operating time. Energy saving options range from continuous mixing with low power densities of 1 W m-3 to mixing by means of short, intense energy pulses (impulse aeration, impulse stirring). However, the following correlation applies: the shorter the duration of energy input, the higher the power density on the respective volume-specific energy consumption isoline. Under favourable conditions with respect to tank volume, tank geometry, aeration and agitator position, mixing energy can be reduced to 24 Wh m-3 d-1 and below. Additionally, it could be verified that power density of agitators stands in inverse relation to tank volume.