Digestion Of Wastewater Sludge Research Articles

Experimental Investigation and Classification of Wastewater Treatment Sludge as Pozzolan for Cement

This paper presents an investigation conducted to evaluate wastewater treatment sludge for potential use as a cement extender or pozzolan. Two varieties comprising the digested wastewater sludge (DWWS) and activated wastewater sludge (AWWS) materials, were finely ground then calcined at 750 °C for 30 min. Subsequently, the calcined sludge waste materials were blended with ordinary Portland cement CEM I 52.5 N at 0, 10, 20, 30% DWWS or AWWS, and used to prepare mortar mixtures at proportions of 1:3:0.61 cement to sand to water. Various tests were conducted including workability, compressive strength, pozzolanic activity with lime, drying shrinkage and alkali-silica reaction. It was found that both varieties of the sludge waste materials, once blended with CEM I at 20% DWWS or 20% AWWS, satisfied the ASTM C618 criteria for Class C pozzolan, and may be classified as CEM II /A-P 32.5 N,R cement type of EN 197-1/SANS 50197-1. The overall performance of DWWS was relatively better than that of AWWS.

Petroleum coke supplementation for enhanced biogas production and phosphate removal under mesophilic conditions.

The use of carbon-based conductive materials has been shown to lead to an increase in biogas and methane yields during anaerobic digestion (AD). The effect of these additives on AD using synthetic substrates has been extensively studied, yet their significance for wastewater sludge digestion has not been adequately investigated. Therefore, the aim of this research was to optimize the concentration of petroleum coke (PC) that is a waste by-product of oil refineries, for the anaerobic digestion of wastewater sludge and investigation of phosphate removal in the AD process in the mesophilic temperature range. According to the results of the experiments, supplementing reactors with PC could significantly improve biogas and methane production. Supplementation of reactors with 1.5 g/L PC led to 23.40 ± 0.26% and 42.55 ± 3.97% increase in biogas production and methane generation, respectively. Moreover, the average volatile solids (VS), phosphate, and chemical oxygen demand (COD) removals were 43.43 ± 0.73, 46.74 ± 0.77%, and 60.40 ± 0.38%, respectively.

Anaerobic Digestion of Wastewater Sludge for Improved Energy Recovery: Alkaline Pretreatment Impact, Digestate Quality Assessment, and Reactor Design

Anaerobic Digestion of Wastewater Sludge for Improved Energy Recovery: Alkaline Pretreatment Impact, Digestate Quality Assessment, and Reactor Design

Digested wastewater sludge dewatering process using water treatment plants chemical sludge and walnut shell activated carbon powder

Digested wastewater sludge dewatering process using water treatment plants chemical sludge and walnut shell activated carbon powder

Kinetic Modeling of Methane Production from the Anaerobic Digestion of Wastewater Sludge from a Treatment Plant in Kenitra, Morocco

Kinetic Modeling of Methane Production from the Anaerobic Digestion of Wastewater Sludge from a Treatment Plant in Kenitra, Morocco

Variations in the extraction and clean-up efficiency of DNA during anaerobic digestion of wastewater sludge at mesophilic and thermophilic temperatures

The effect of anaerobic sludge digestion on the isolation of DNA and clean-up efficiency of obtained DNA isolates was studied. Influent and digestate of a continuous full-scale reactor were sampled twice. Also, batch digesters were operated at 35, 45 and 55 °C, namely, AnD.35, AnD.45 and AnD.55. The batch reactors were sampled at 3-to-4-day time intervals during the digestion. A sharp decline in the extraction yield was observed over time for the batch reactors. In AnD.55, the extraction yield declined by 96 % in 12 days. The purity of the DNA isolates was assessed by purity ratios, which included absorption at 260 nm to that at 280 nm (Abs260/280) and to that at 230 nm (Abs260/230). Abs260/230 before clean-up declined as a result of digestion in all reactors, the most severe case being AnD.55 decreasing from 1.91 to 0.47 in nine days. The efficiency of clean-up was evaluated by analysing DNA recovery and changes in the purity ratios. AnD.35 and the full-scale reactor had the highest recoveries (≥ 80 %). Furthermore, a 4.1-fold increase was observed in Abs260/230. Additionally, non-linear correlations were found between purity parameters and the DNA concentration (R2 > 0.7). The observations of the current investigation strongly indicate that the change in DNA extraction yield was at least partly due to the change in DNA extraction efficiency and not just the change in the actual DNA content. This is an important consideration for the quantification of biomass, specific genes, and microbial populations, where DNA isolation plays a key role.

Upgrading Anaerobic Sludge Digestion by Using an Oil Refinery By-Product

Carbon-based conductive additives have been studied for their positive effects on anaerobic digestion (AD) using synthetic substrates, but their importance in wastewater sludge digestion has not been sufficiently explored. This research investigated and compared the effects of two conductive materials (graphene and petroleum coke) with and without trace metal supplementation. The results indicated that supplementing reactors with graphene and petroleum coke could significantly improve biogas production. The supplementation of 1 g/L petroleum coke and 2 g/L graphene, without trace metal addition, led to an increase in the biogas production by 19.10 ± 1.04% and 16.97 ± 5.00%, respectively. Thus, it can be concluded that petroleum coke, which is an oil refinery by-product, can be used to enhance biogas production in a similar way to other carbon-based conductive materials that are currently available on the market. Moreover, using petroleum coke and graphene, the average chemical oxygen demand (COD) removal was 42.84 ± 1.23% and 42.80 ± 0.45%, respectively, without the addition of trace metals. On the other hand, supplementation of the reactors with trace elements resulted in a COD removal of 34.65 ± 0.43% and 34.05 ± 0.45% using petroleum coke and graphene, respectively.

Development of non-linear empirical models to estimate the abundance of carbapenem resistance genes during anaerobic digestion of wastewater sludge at mesophilic and thermophilic temperatures

Antibiotic resistance genes (ARGs) encode resistance against antibiotic drugs in bacteria. Carbapenem antibiotics are one of the last lines of defence against bacterial infections and carbapenem resistance genes (CRGs) accumulate in sludge during wastewater treatment. Anaerobic digestion is the most used method for sludge treatment, and it is important to know the abundance and removal of CRGs in anaerobically digested sludge before land application due to their public health relevance. However, gene quantification is time-consuming, costly, and sensitive to contamination. Previous research indicates a nexus between ARGs, solids, and nutrients in sludge. This study aimed to develop multiple regression models to estimate the abundance of CRGs from solids and nutrient concentrations in sludge, which are routinely measured for the monitoring and design of anaerobic digesters. Batch and continuous reactors were operated at mesophilic and thermophilic temperatures. Sludge samples were taken during digestion. CRGs (blaGES, blaOXA-48 and blaIMP-27), 16S rRNA and integron class 1 were quantified. Solids, chemical oxygen demand, orthophosphate and ammonia were measured as well. Anaerobic digestion reduced the quantity of the genes. First and second-order Kinetic rate constants (K1 and K2) were affected by temperature, and K1 absolute value followed the order blaOXA-48 > blaGES > Int 1. Multiple regression modelling was conducted in linear (LM) and non-linear (NLM) modes. This study presents the first NLM models to simulate the quantities of CRGs during anaerobic digestion of wastewater sludge at mesophilic and thermophilic temperatures. Adjusted R2 ranged 0.352–0.988 and 0.916–0.996 for the LM and NLM models, respectively. NLM models estimated the gene abundance more accurately than LM models, and they may be useful for researchers and practitioners to estimate the removal rate of target genes under different operational conditions.

Finham gas-to-grid plant, UK: delivering a multi-disciplinary renewable energy scheme

Finham ‘gas-to-grid’ project near Coventry, UK produces renewable bio-methane from the biogas generated by anaerobic digestion of wastewater sludge. Completed in 2021, the plant now exports bio-methane to the gas grid, contributing to ‘decarbonisation’ of gas supply and helping to deliver water utility Seven Trent’s 2030 net-zero-emissions goals. This paper focuses on the innovative solutions adopted to maximise production of bio-methane, the plant procurement and delivery process, and the challenges of Covid-19, Britain’s exit from the European Union and site-specific constraints.

A mathematical model for the kinetics of concurrent volatile solids destruction and water evaporation during aerobic and anaerobic digestion of wastewater sludge under mesophilic and thermophilic temperatures

Experimental and computational approaches were employed to model kinetics of volatile solids destruction in the presence of water evaporation during biological digestion of wastewater sludge. Water evaporation occurred in both anaerobic and aerobic laboratory digesters with a much higher intensity in the latter. The water evaporation followed a linear trend over time. By inclusion of the linear equation for water evaporation rate, new kinetic models were developed to predict volatile solids (VS) and volatile suspended solids (VSS) concentrations of batch biological digesters. Modelled results using a first-order model were in good agreement with the measured VS concentrations of the anaerobic reactors operated at 35 °C and 55 °C (AnD.55) with coefficients of determination (R2) 0.92 and 0.84, respectively. VS degradation of AnD.55 was slightly more consistent with zero-order kinetics (R2 = 0.86). VS and VSS concentrations measured for batch aerobic digesters also agreed with the first-order model. R2 values were 0.91, 0.75 and 0.99 for reactors operated at 35 °C (AD.35), 45 °C and 55 °C, respectively. As for the progression in terms of VSS concentration, the highest R2 and lowest sum of squared error values belonged to AD.35. This is the first study that developed kinetic models for simultaneous VS degradation and water evaporation under both mesophilic and thermophilic conditions. The outcomes of this study indicate that water evaporation needs to be considered for accurate determination of the kinetic rate constant and solids reduction in laboratory and full-scale sludge digesters.

Variations in the Extraction and Clean-Up Efficiency of DNA Isolates During Anaerobic Digestion of Wastewater Sludge at Mesophilic and Thermophilic Temperatures

Variations in the Extraction and Clean-Up Efficiency of DNA Isolates During Anaerobic Digestion of Wastewater Sludge at Mesophilic and Thermophilic Temperatures

Relationship between ultraviolet-visible spectra and soluble species in the liquid phase of wastewater sludge during biological digestion under mesophilic and thermophilic conditions

Absorption of ultraviolet (UV)-visible (Vis) light by the liquid phase of wastewater sludge during biological digestion was studied. Sludge samples were obtained from batch anaerobic and aerobic digestion experiments conducted at mesophilic and thermophilic temperatures, as well as influent and effluent of a full-scale anaerobic digester. In tandem with acquiring the UV-Vis spectra, the concentration of soluble parameters was measured. Integrated areas under the spectra in the UV and Vis regions were calculated as AUV and AVis, respectively. For the batch experiments, the computed areas increased with digestion time. In addition, a power-law function was able to describe the correlation between soluble chemical oxygen demand (SCOD) concentration and AUV for anaerobic digestion at 35 °C and 45 °C, and aerobic digestion at 55 °C. Coefficients of determination (R2) for the mentioned cases were between 0.812 and 0.933. Furthermore, power-law functions also described a correlation between SCOD and soluble ortho-phosphate concentrations during batch anaerobic digestion at 35 °C (R2 = 0.921) and 45 °C (R2 = 0.812). Moreover, analysis of the data obtained from the aerobic digestion experiment suggests that the mass of UV-absorbing matter linearly decreased over time during aerobic digestion at 45 °C (R2 = 0.925) and 55 °C (R2 = 0.996). The outcomes of the current study indicate that the integrated area under the UV spectrum of sludge filtrates reflects the progression of biological digestion of wastewater sludge under thermophilic and mesophilic conditions, which can be used for process monitoring and optimization.

Anaerobic Digestion of Wastewater Sludge and Alkaline-Pretreated Wheat Straw at Semi-Continuous Pilot Scale: Performances and Energy Assessment

During the last decade, the application of pretreatment has been investigated to enhance methane production from lignocellulosic biomass such as wheat straw (WS). Nonetheless, most of these studies were conducted in laboratory batch tests, potentially hiding instability problems or inhibition, which may fail in truly predicting full-scale reactor performance. For this purpose, the effect of an alkaline pretreatment on process performance and methane yields from WS (0.10 g NaOH g−1 WS at 90 °C for 1 h) co-digested with fresh wastewater sludge was evaluated in a pilot-scale reactor (20 L). Results showed that alkaline pretreatment resulted in better delignification (44%) and hemicellulose solubilization (62%) compared to untreated WS. Pilot-scale study showed that the alkaline pretreatment improved the methane production (261 ± 3 Nm3 CH4 t−1 VS) compared to untreated WS (201 ± 6 Nm3 CH4 t−1 VS). Stable process without any inhibition was observed and a high alkalinity was maintained in the reactor due to the NaOH used for pretreatment. The study thus confirms that alkaline pretreatment is a promising technology for full-scale application and could improve the overall economic benefits for biogas plant at 24 EUR t−1 VS treated, improve the energy recovery per unit organic matter, reduce the digestate volume and its disposal costs.

Ammonia separation from wastewater using bipolar membrane electrodialysis

AbstractNitrogen pollution is a serious environmental challenge in natural water and thus selective ammonia separation in wastewater treatment is of great importance to decrease the nitrogen load to natural water systems. Bipolar membrane electrodialysis (BMED) is a relatively new ion exchange membrane technology that can be used for ammonia recovery from wastewater as a beneficial substance. A bench‐scale BMED stack with seven pairs of bipolar membrane (BPM) and a cation exchange membrane (CEM) was operated under various voltage applications to separate ammonia from dewatering centrate (liquid downstream from dewatering of anaerobically digested wastewater sludge). Ammonia in the wastewater was rapidly separated (up to 87% in 30 min) and recovered as ammonium hydroxide solution using the BMED stack. We found that the maximum rate of ammonium separation was governed by the concentration polarization near CEMs rather than water transport into BPMs. In addition, even with the significantly high organic level in dewatering centrate (408 mg/L as total suspended solids), high efficient ammonia separation was maintained over 8 repeated BMED operations without any pretreatment of the feed wastewater, indicating effective organic fouling control with regular chemical cleaning. Furthermore, BMED operation for 30 minutes at 5.0 V per cell pair was found to be ideal for high purity ammonium hydroxide production and low electrical energy consumption. Based on the high separation efficiency and low energy consumption, we suggest that BMED be further investigated as an attractive option for ammonia separation and recovery from wastewater.

Dynamics of Biological Processes during Composting of Anaerobically Digested Wastewater Sludge

Microbiological processes occurring in the course of controlled thermophilic composting of dehydrated wastewater sludge anaerobically digested in a reactor at the Lyubertsy waste treatment plant (Moscow, Russia) were studied. Dynamics of the concentrations of nitrogen species in the presence of microorganisms of the nitrogen cycle (ammonifying, nitrifying, denitrifying, and nitrogen-fixing) was studied at the changed temperature modes at sequential stages of long-term composting (98 days). During the active stage of composting, considerable emission of ammonia (553–861 mg m–3) and nitrogen oxide (67–86 mg m–3) were observed on days 6–10; these values significantly exceeded the accepted allowances for atmospheric emissions. Abundance of culturable heterotrophic microorganisms, CFU numbers of nitrogen-fixers, and the presence and activity of cultured nitrifying and denitrifying microorganisms were determined using microbiological techniques. The data of real-time PCR and NGS profiling by the 16S rRNA genes were used to analyze the taxonomic diversity of the microorganisms involved in composting (bacteria, archaea, and fungi); the patterns of succession within the microbial community during this process were established. Laboratory experiments revealed the potential for further decomposition of organic matter of digested sludge, which was probably unavailable to microorganisms under anoxic conditions, but could be degraded by the aerobic microbiota, resulting in a product stimulating plant growth and containing 2.3% of total nitrogen and containing ammonium and nitrate nitrogen (890 and 3750 mg kg–1, respectively).

Fluorescence intensity, conductivity, and UV–vis absorbance as surrogate parameters for real-time monitoring of anaerobic digestion of wastewater sludge

Traditional wastewater treatment monitoring techniques are time-intensive and do not allow real-time process control, creating a need for methods capable of rapid assessment. As such, the objective of this research was to develop and test new methods to measure surrogate wastewater and sludge characterization parameters (conductivity, fluorescence intensity, and UV–vis absorbance) and evaluate each parameter’s suitability for real-time assessment of treatment progression and performance. Anaerobic digestion of mixed primary and secondary sludge was carried out in a continuous reactor over 28 days. COD (chemical oxygen demand), TS/VS (total solids/volatile solids), pH, conductivity, UV–vis absorbance, and fluorescence intensity were measured over the treatment period and linear regressions between surrogate parameters and COD and VS were performed to identify potential relationships. Regression analyses yielded strong correlations between COD and conductivity, fluorescence intensity (FI), and UV–vis absorbance (R2 values of 0.84, 0.72, 0.74 respectively), and between VS versus conductivity and UV–vis absorbance (R2 values of 0.68, 0.73 respectively) illustrating their potential as real-time monitoring tools. It was also possible to evaluate the progression of treatment by monitoring the point of changes in the trends of the surrogate parameters.

Investigating the impact of inoculum source on anaerobic digestion of various species of marine macroalgae

This study investigated the intrinsic biodegradation potential of marine organic sediment for effective biogas production from various species of marine macroalgae and non-marine biomass. Biogas production potential tests were carried out on three species of seaweed harvested from the west coasts of Scotland, Laminaria digitata, Fucus serratus, and Saccharina latissima, and on a non-marine cellulose biomass seeded with uncultivated and unadapted anoxic marine sediments. As a comparison, the same experiments were repeated using the same substrates but seeded with active mesophilic anaerobically digested sewage sludge. For the cultures seeded with anoxic marine sediments, the highest methane yield was observed in both L. digitata and S. latissima cultures while F. serratus and cellulose, cultures performed relatively poorly. For those seeded with digested sludge, all cultures performed relatively well, except F. serratus. These results show that marine sediments can be effective inoculum for seaweeds digestion. Phylogenetic analyses of the methanogenic community in both sources of inoculum showed that the methanogen community within the sediment and sludge seeded cultures were different. Each culture was dominated by methanogenic populations suitable for the utilisation of the specific biomass derivatives and environmental conditions. For instance, members of the genus Methanosaeta which, dominated sludge seeded cultures were not detected in the sediment seeded cultures. A similar occurrence was observed for the genus Methanofollis which was only detected in the sediment seeded cultures. Hence, in areas where seaweed forms part of a co-digestion with non-marine biomass, start-up using a mixture of anoxic marine sediments and digested wastewater sludge has the potential to provide greater process stability and robustness than using either as sole inoculum.

Антимикробные свойства биоцида на основе четвертичных аммонийных соединений и полигексаметиленгуанидина и потенциальные способы его дезактивации

Biocidal agents (BA) are widely used in environmentally safe toilet complexes (ESTC) of passenger railcars to suppress microbial activity in fаecal sludge (FS). Subsequent disposal of BA-containing FS at municipal sewage treatment facilities adversely affects their work due to the loss of activated sludge. The antimicrobial properties of BA, based on quaternary ammonium compounds (QAC) and polyhexamethylene guanidine (PHMG), as well as methods for its neutralization, have been studied. It was confirmed that BA based on QAC and PHMG has an antimicrobial effect on various groups of bacteria, reducing their number by 10-100 or more times. It was found that FS contains two groups of microorganisms with different sensitivity to BA. Methods for deactivation of the BA antimicrobial action in FS were tested using: (1), a deactivating agent; (2), incubation with thermophilically digested wastewater sludge as a source of the microbial methanogenic community; and (3), chemical deactivation by acidification or alkalization. The highest efficiency was shown by the method of deactivation of BA via thermophilic anaerobic digestion with pretreatment of FS with a strong acid biocide, fаecal sludge of ESTC of passenger railcars, antimicrobial activity, quaternary ammonium compounds, polyhexamethylene guanidine, deactivator, methanogenic microbial community This work was financially supported by the Ministry of Science and Higher Education of the Russian Federation.

Importance of 2,4,6-Trichloroanisole (TCA) as an odorant in the emissions from anaerobically stabilized dewatered biosolids

Odours from stabilized biosolids after anaerobic digestion of wastewater sludge can cause local community impact. Apart from the well-known odorants such as sulfur compounds, contributions from other volatile organic compounds (VOCs) to nuisance odours is limited. The presence of compounds with low odour detection thresholds (ODTs) at low concentrations, can present challenges for analytical identification. Thirty-six biosolids samples were taken after anaerobic stabilisation and dewatering at a wastewater treatment plant, Sydney, Australia. Biosolid cake samples were stored outside in loosely covered trays under aerobic conditions, however without interactions with soil microorganisms as it would be in reality. All biosolids cake samples were analysed over a period of 35 days. Emissions were collected onto Tenax TA sorbent tubes using a U.S. EPA flux hood method at storage days 1, 3, 7, 10, 14, 21 and 35. Gas chromatography (GC) coupled with mass spectrometer detector (MSD) and an olfactory detection port (ODP) was used to identify a musty/moldy/earthy type odorant in the biosolids emissions as 2,4,6-trichloroanisole (TCA). Measured odour intensities, classified on a scale from 1 to 4, and odour characters were specified by three ODP assessors. TCA was identified in all biosolid cake emissions. The measured odour intensities of the TCA did not significantly alter as the biosolids were aged, however varied between biosolids cakes. Due to its odour intensity, 85% frequency of detection and its low ODT, which is orders of magnitudes lower than sulfur compounds, TCA should be considered as a potential odorant of concern in biosolids emissions.

Anaerobic digestion and biogas beneficial use at municipal wastewater treatment facilities in Colorado: A case study examining barriers to widespread implementation

In 2004 the state of Colorado became the first state in the U.S. to implement a renewable energy standard. Electrical utilities have met the state's energy goals using a combination of wind, hydroelectric, and solar power, while giving relatively little consideration to biogas generated from domestic wastewater treatment (i.e., biomass accounts for < 0.1% of renewable energy used in Colorado). An examination of wastewater treatment facilities designed to treat flowrates >7570 m3d-1 indicates that energy generated from the anaerobic digestion of wastewater sludge and combined heat and power technologies is limited in Colorado. At the time of this study, only 39% of examined facilities used anaerobic digestion and only 4 of 24 anaerobic digestion facilities actively employed combined heat and power. Barriers to widespread implementation of anaerobic digestion and combined heat and power were primarily associated with costs, e.g., infrastructure or equipment capital costs; however, other barriers were identified, including: effectiveness of available grant and loan programs, state-level regulations, electric utility rate structures, the influence of local decision-making authorities, and a reluctance by wastewater treatment facilities to change sludge digestion practices. To overcome these barriers, recommendations for the state of Colorado include: initiate a comprehensive program focused on promoting current incentives, review the efficacy of available incentive programs and make long-term modifications, enact regulatory updates, increase education and outreach, and establish a program to promote co-digestion of wastewater sludge with other organic waste streams. This state-level case study explores a large number of facilities at a granular level, the results of which may be relevant to other states or regions and can provide insight into barriers elsewhere.