Sludge Liquor Research Articles

Combining Shift to Biogas Production in a Large WWTP in China with Optimisation of Nitrogen Removal

Despite the huge current challenges in sewage sludge treatment and disposal in China, anaerobic sludge stabilisation (AnSS) is still not a state-of-the-art process in WWTP in the country. However, the potential benefits of anaerobic sludge stabilisation may outweigh the drawbacks. One of these drawbacks is the backload from the sludge liquor that increases the nutrient load in the biological treatment stage. This work shows via computer modelling that not only can the sludge production and disposal costs be significantly reduced, but also that, with sensible automation and operational strategies (e.g., bypass of primary clarifiers, use of a centrate dosing strategy, incorporation of ammonium nitrogen sensors, etc.), the effects of the backload can be counteracted for nitrogen removal, even considering that wastewater in China often has an unfavourable C/N ratio for nitrogen removal. The tested strategies would even improve the overall plant performance in terms of norm compliance, sludge production, energy use, and energy production

Enhanced aerobic granular sludge formation by applying Phanerochaete chrysosporium pellets as induced nucleus.

The long start-up period is a major challenging issue for the widespread application of aerobic granular sludge (AGS). In this study, a novel rapid start-up strategy was developed by inoculating Phanerochaete chrysosporium (P. chrysosporium) pellets as the induced nucleus in a sequencing batch airlift reactor (SBAR) to enhance activated sludge granulation. The results demonstrated that P. chrysosporium pellets could effectively shorten the aerobic granulation time from 32 to 20days. The AGS promoted by P. chrysosporium pellets had a larger average diameter (2.60-2.74mm) than that without P. chrysosporium pellets (1.78-1.88mm) and had better biomass retention capacity and sedimentation properties; its mixed liquor suspended solids (MLSS) and sludge volume index (SVI30) reached approximately 5.2g/L and 45mL/g, respectively. The addition of P. chrysosporium pellets promoted the secretion of extracellular polymeric substances (EPS), especially protein (PN). The removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) in P. chrysosporium pellets reactor were 98.91%, 89.17%, 64.73%, and 94.42%, respectively, which were higher than those in the reactor without P. chrysosporium pellets (88.73%, 82.09%, 55.75%, and 88.92%). High throughput sequencing analysis indicated that several functional genera that were responsible for the formation of aerobic granules and the removal of pollutants, such as Acinetobacter, Pseudomonas, Janthinobacterium, and Enterobacter, were found to be predominant in the mature sludge granules promoted by P. chrysosporium pellets.

Engineering pressure retarded osmosis membrane bioreactor (PRO-MBR) for simultaneous water and energy recovery from municipal wastewater

Osmotic membrane bioreactors (OMBR) have gained increasing interest in wastewater treatment and reclamation due to their high product water quality and fouling resistance. However, high energy consumption (mostly by draw solution recovery) restricted the wider application of OMBR. Herein, we propose a novel pressure retarded osmosis membrane bioreactor (PRO-MBR) for improving the economic feasibility. In comparison with conventional FO-MBR, PRO-MBR exhibited similar excellent contaminants removal performance and comparable water flux. More importantly, a considerable amount of energy can be recovered by PRO-MBR (4.1 kWh/100 m2·d), as a result of which, 10.02% of the specific energy consumption (SEC) for water recovery was reduced as compared with FO-MBR (from 1.42 kWh/m3 to 1.28 kWh/m3). Membrane orientation largely determined the performance of PRO-MBR, higher power density was achieved in AL-DS orientation (peak value of 3.4 W/m2) than that in AL-FS orientation (peak value of 1.4 W/m2). However, PRO-MBR suffered more severe and complex membrane fouling when operated in AL-DS orientation, because the porous support layer was facing sludge mixed liquor. Further investigation revealed fouling was mostly reversible for PRO-MBR, it exhibited similar flux recoverability (92.4%) to that in FO-MBR (95.1%) after osmotic backwash. Nevertheless, flux decline due to membrane fouling is still a restricting factor to power generation of PRO-MBR, its power density was decreased by 38.2% in the first 60 min due to the formation of fouling. Overall, in perspective of technoeconomic feasibility, the PRO-MBR demonstrates better potential than FO-MBR in wastewater treatment and reclamation and deserves more research attention in the future.

Unrevealing the role of in-situ Fe(II)/S2O82- oxidation in sludge solid–liquid separation and membrane fouling behaviors of membrane bioreactor (MBR)

Membrane bioreactor (MBR) has received continuous attention in waste activated sludge treatment, however, membrane fouling still remains a big and inevitable challenge to its wide applications. Ferrous-persulfate (Fe(II)/S2O82–) oxidation possesses the outstanding oxidizing capability and high-efficiency in degrading refractory organics and enhancing sludge solubilization. In this study, in-situ Fe(II)/S2O82- oxidation was coupled for pretreating sludge, and the effect on the subsequent filtration performance and membrane fouling behaviors in MBR was investigated. Fe(II)/S2O82- oxidation had an outstanding effect on enhancing filterability of mixed sludge liquor and alleviating membrane fouling. Under the optimal pretreatment condition of 1.5/1.2 mmol-Fe(II)-S2O82-/g-VS, the membrane flux of reactor reached 20.6 mL/s/m2, and a 46.6% decrease in trans-membrane pressure (TMP) was obtained compared to the raw sludge without pretreatment. Correlation analysis reveal that polysaccharides in extracellular polymeric substances was the decisive factor affecting the membrane fouling behavior. The strong oxidizing ability of in-situ Fe(II)/S2O82- pretreatment could effectively break the glutinous and pilotaxitic biopolymer matrix deposited on the membrane surface, and rupture the hydrophilic bonds of proteins and polysaccharides. The high molecular weight biopolymers were brought down, with the water bounded inside the flocs released into liquid phase. Iron-mediated coagulation was also conductive to the re-aggregation of the fine particles and subsequent membrane fouling control. For raw sludge, the predominated fouling mechanisms were intermediate pore blocking and cake layer formation, while complete pore blocking and standard pore blocking occurred more frequently for pretreated sludge. This work provides a promising approach based on Fe(II)/S2O82- oxidation processes for efficient abatement of membrane fouling and sludge treatment.

Alkaline thermal hydrolysis of sewage sludge to produce high-quality liquid fertilizer rich in nitrogen-containing plant-growth-promoting nutrients and biostimulants

To produce liquid fertilizer containing nitrogen-containing plant-growth-promoting nutrients (N-PGPN) and plant-growth-promoting biostimulants (N-PGPB) from sewage sludge is attracting increasing interest recently, due to its superb fertilizing effect and the ease of application. Thus, this study aims to investigate the feasibility of producing high-quality liquid fertilizer with N-PGPN and N-PGPB recovery through alkaline thermal hydrolysis (ATH) using Ca(OH)2. Results suggested that ATH treatment was superior in N solubilization (TSN/TN > 54%) and organic N maintenance in sludge liquor (> 80%) when compared to single thermal hydrolysis (TH). More surprisingly, ATH also promoted the production of N-PGPN and N-PGPB. As for N-PGPN, the maximum free amino acids (FAAs) accumulation in ATH liquor was 56.82 g/L at 120 °C while soluble protein (SPN) and soluble humic acid (SHA) reached 8.30–8.88 g/L and 1.88–2.05 g/L at 140–160 °C. The greatest N-PGPB produced by ATH treatment was achieved at 160 °C, with the detection of 1.156 mg/L phytohormones (indole-3-acetic acid and hydroxyphenyl acetic acids) and 4.95 mg/L allelochemicals (indolic derivatives and aromatic carboxylic acids). The 2D correlation FTIR maps analyses suggested, compared with TH, ATH could achieve protein hydrolysis before polysaccharides solubilization and denaturation with the temperature increased, thus avoiding Maillard reaction and benefiting N-PGPB production. Moreover, the laboratory investigation and field study indicated the usage of ATH liquor improved the growth of plants without inducing heavy metal contamination and soil salinization. Hence, ATH is a promising technology to produce high-quality liquid fertilizer rich with N-PGPN and N-PGPB from sewage sludge, especially suitable for such sludge with a low VS/TS ratio where biological treatment is inapplicable.

Production of intracellular lipids from thermally hydrolyzed waste sludge by oleaginous yeast for energy and resource recovery

Municipal wastewater treatment plants generate large quantities of sludge every day, and the disposal of the waste sludge is one of the most challenging and expensive burdens for megacities. However, the rich organic content in sludge should be recovered and utilized rather than wasted. In this study, an innovative sludge treatment technology is developed for converting waste sludge into bio-lipids for energy and resource recovery. The technology uses thermal hydrolysis (TH) for the pretreatment of the sludge, following which the supernatant liquor of the hydrolyzed sludge is used as the substrate for the cultivation of oleaginous yeast to produce intracellular bio-lipids. TH pre-treatment resulted in the release of 36.8% of the organics from the sludge into the supernatant, which is more effective than acid, ultrasound, and alkaline sludge pretreatments. By fermentation using Trichosporon dermatis, approximately 8.2% of the organics in the TH sludge liquor was transformed into bio-lipids within one day of cultivation. An acidic condition with a process pH of 3.5–4.5 was found to be favorable for the growth of T. dermatis. Moreover, glucose was added to the TH sludge liquor to provide a co-substrate of organics and nutrients for fermentation, which created a favorable acidic condition (pH 3.5–4.0) for oleaginous yeast and improved the conversion of organics into bio-lipids to 12.8%. The produced bio-lipids comprised fatty acids ranging from C16 to C25, with a high proportion of unsaturated fatty acids (C18:1 and C18:2 > 65.0%). Based on the experimental results, a two-step scheme is proposed, which involves fermentation of the sludge liquor with oleaginous yeast for bio-lipid production followed by anaerobic digestion of the solid phase and organic residues for biogas production. The proposed scheme can help achieve the value-added recovery of organic resources from waste sludge.

Occurrence and Distribution of Antibiotic Resistance Genes in Municipal Wastewater Treatment Plants with D-Type Filters

Filters are popularly used in municipal wastewater treatment plants (WWTPs) as the final guards against effluent solids; however, their impacts on antibiotic resistance gene (ARG) removal in the WWTPs are still unclear. In this study, metagenomic analysis was used to find out the distribution characteristics of ARGs in two WWTPs equipped with the same D-Type fiber filters. Samples of influent, activated sludge liquor, secondary clarifier effluent, and D-Type filter effluent were found to host 695, 609, 675, and 643 ARG subtypes, respectively. The detected ARGs mainly included macB (4.1–8.9%), sav1866 (1.7–3.4%), and oleC (1.6–3.8%). Co-occurrence network analysis combined with contribution analysis helped to identify the ARG-related risks in the samples. Microbacterium, Acinetobacter, Gordonia, and Streptomyces significantly correlated with more than ten kinds of ARG subtypes, implying that they are potential hosts for these resistance gene subtypes. The number of ARG subtypes in the D-Type filter was less than those in the secondary clarifier effluent, indicating the potential of D-Type filters to effectively reduce the ARGs released into the environment. However, the abundance of two pathogens, Mycobacterium and PmrA, increased after the treatment by the D-Type filter, which may reveal the adverse effects of intercepting ARGs inside the fibers. The results may help the understanding of the complex role of the D-Type fiber filter on ARG distribution in WWTPs.

Exposure to stressful conditions alters the properties and fouling behavior of suspended microparticles in anaerobic processes

Microparticles, a type of suspended particles in anaerobic membrane bioreactors (AnMBRs) with a size ranging from 0.45 to 10 µm, play a vital role in fouling. Here, the occurrence, composition, and fouling behavior of microparticles were determined during the cultivation of anaerobic sludge under stressful conditions that included high sulfate (3 g/L), high ammonium (3 g/L), high temperature (55 °C), and high salinity (28 g NaCl/L) tests. The results showed that the total organics in the supernatant of anaerobic sludge liquor increased after exposure to high temperature and high salinity, and the proportion of microparticles decreased significantly compared with that of the control, which could be due to the decreasing ratios of live/dead cells in the microparticles, thereby producing more soluble organics (< 0.45 µm). Accordingly, dead-end filtration tests showed that the supernatants with the same organic concentration in high temperature and high salinity groups had a decreasing fouling potential. Based on Hermia’s model, the cake filtration model fitted the supernatant filtration data under all stressful conditions. Moreover, the high-temperature group also fitted well with the pore-blocking model. The correlation between fouling parameters and the microbial species of microparticles suggested the potential contributions of Bacteroidales, Aminicenantales, Anaerolineales, and Caldisericales to cake/gel fouling, and the positive effects of Ignavibacteriales and Syntrophobacterales on pore blocking. Overall, exposure to stressful conditions considerably altered the production and characteristics of microparticles during the anaerobic digestion, thus leading to different fouling mechanisms in AnMBRs.

Investigation of direct waste‐activated sludge dewatering benefits and costs in a water resource recovery facility

Dewatering of anaerobic digested (AD) sludge containing waste-activated sludge (WAS) from enhanced biological phosphorus removal (EBPR) poses numerous challenges including poor dewaterability, struvite scale formation, and recycling of high N and P levels in the sludge liquor to the treatment process. A full-scale water reclamation facility was investigated to mitigate these problems by experimenting with direct dewatering of EBPR WAS, bypassing the AD step. The investigations experimented with various blends of AD primary sludge with undigested thickened WAS to achieve dewatering performance improvements and overall operational cost savings. Direct thickened WAS dewatering has had many positive impacts including enhanced sludge cake solids concentration, reduced chemical use for facility operations, reduced struvite scaling, reduced biogas conditioning media servicing, eliminated need for centrate treatment, recovered capacity of existing unit operations including anaerobic digesters, and eliminated several proposed capital improvement projects that were previously deemed necessary. Although bypassing of WAS to AD reduced total biogas production, the specific gas yield increased to meet all of the facility's biogas demands and minimized excess gas flaring. The overall biosolids production mass increased causing increased transportation costs for disposal and caused notable odors, both of which are being currently investigated. PRACTITIONER POINTS: Direct WAS dewatering bypassing anaerobic digestion yields operational and process benefits in an EBPR water resource recovery facility Dewatered cake solids were increased compared with combined primary and WAS anaerobic digestion and dewatering Nutrient loads in sludge processing returns streams and operational costs are reduced by direct WAS dewatering.

Phosphorus and humic acid extraction from fermentation liquor of ferric phosphate sludge via layered double hydroxides: Efficiency and interaction mechanism

Iron salts are increasingly employed in wastewater treatment worldwide, generating ferric phosphate sludge with low phosphorus (P) bioavailability. The fermentation of ferric phosphate sludge effectively transfers P from the solid phase to the liquid phase and simultaneously releases high contents of ferrous cations (Fe2+) and humic acids (HA) into the sludge liquor. This study aimed to extract P from simulated and real sludge fermentation liquor via Mg/Al layered double hydroxide (LDH), evaluate the impact of co-existed Fe and explore the interaction mechanism between phosphate and HA adsorption. The Fe influence experiments explored the suitable organic matter concentration range for the LDH adsorbent to extract P without the concurrent precipitation of iron compounds. Thus, the residual ferrous species in sludge liquor can be reused as a flocculant. Moreover, the analysis of the adsorption kinetics of phosphate at 25, 35, and 55 °C showed that increasing temperature accelerated the phosphate adsorption rate but had minor effects on the P adsorption capacity. HA and phosphate were jointly adsorbed onto Mg/Al LDH. Investigations on isotherm, kinetics, and mechanism suggested that phosphate anions have a competitive advantage in the ion exchange process but are hindered by large-molecular-weight HA in surface adsorption because of limited adsorption sites. Subsequent adsorption experiments in sludge liquor and nutrient release test confirmed the possibility of using Mg/Al LDH to simultaneously recover P and organic matters from sludge fermentation liquid based on its stable P adsorption performance and intercalated anion slow-release property.

Contactless membrane distillation for effective ammonia recovery from waste sludge: A new configuration and mass transfer mechanism

Membrane distillation (MD) is an attractive technology to remove and recover ammonia (NH3) from waste sludge; however, it suffers from membrane fouling problems. In this study, a contactless MD system was developed by introducing an air gap between the hydrophobic membrane and feed solution to largely eliminate the fouling problems. Results show that the overall NH3 transfer coefficient by contactless MD was (1.49 ± 0.05) × 10−5 m/s, more than 7 times greater than that of conventional MD. In continuous operation with a short retention time of 20 min, a high NH3 recovery (>80%) from fermented sludge liquor and a clean membrane without foulant attachment were maintained, while the conventional MD system failed in 12 h due to severe membrane fouling. After NH3 recovery, the sludge liquor was turned into a preferable organic carbon source for utilization. This innovative contactless MD can recover ammonia from various waste liquids.

Pilot Scale Experiments for Ammonium Recovery from Sludge Liquor at a Municipal Waste Water Treatment Plant

Pilot Scale Experiments for Ammonium Recovery from Sludge Liquor at a Municipal Waste Water Treatment Plant

Low-temperature thermal hydrolysis for anaerobic digestion facility in wastewater treatment plant with primary sludge fermentation

Primary sludge (PS) fermentation prior to anaerobic digestion (AD) is becoming more common in wastewater treatment plants (WWTPs) for the production and utilization of volatile fatty acids-rich sludge liquor in biological nutrient removal processes. However, the thermal hydrolysis process (THP) for enhancing AD of sludge in WWTPs with PS fermentation has rarely been investigated. This study examined low-temperature THP (50–90°C, 30–90 min) for enhancing co-digestion of fermented primary sludge (FPS) and thickened waste activated sludge (TWAS). The experiments were conducted under two schemes: scheme-1 (THP of TWAS + FPS) and scheme-2 (THP of TWAS only). Scheme-2 was more effective in solubilizing COD (up to 20.4% increase in SCOD) and various macromolecular compounds (e.g., proteins and carbohydrates). In contrast, scheme-1 was more efficient in VSS solubilization (up to 26.12%). Scheme-1 also resulted in a greater enhancement in methane production over the control (scheme-1: 56.28% at 90°C, 90 min vs. scheme-2: 43.4% at 90°C, 60 min). Thus, these results suggested that low-temperature THP of TWAS alone (scheme-2) would result in solubilization of refractory macromolecular compounds, leading to a relatively lower positive impact on methane yields than scheme-1. The preliminary economic assessment considering THP operating cost, enhancement in energy recovery, and saving in biosolids handling costs indicated that THP at 90°C (90 min) under scheme-1 could provide the highest net saving of $79.55/dry tonne solids compared to the control (AD without THP). These results will provide technical guidance in adopting THP in WWTPs with PS fermentation.

Black liquor increases methane production from excess pulp and paper industry sludge

The aim of the study was to use black liquor produced during the soda pulping process in a pulp and paper mill to increase methane production during pulp and paper industry sludge treatment and decrease the treatment cost. The effects of black liquor on sludge solubilization and methane production were assessed and the economic feasibility of the process was evaluated. Black liquor and NaOH were found to be equivalent in the thermochemical pretreatment process to solubilize sludge and disintegrate flocs. However, adding black liquor increased the background chemical oxygen demand and volatile fatty acid concentration and increased the amount of methane produced by approximately 7–30%. A start-up delay was emphasized by first-order kinetics model due to black liquor addition while methane production remained stable. Economic assessments of five scenarios were performed. It was found to be economically feasible to use black liquor to replace NaOH for the thermal pretreatment process. The surplus methane generated suggested that co-digestion of sludge and black liquor allows surplus bioenergy to be produced during the thermochemical pretreatment anaerobic digestion process.

Hydrothermal treatment and biorefinery of sewage sludge for waste reduction and production of fungal hyphae fibers and volatile fatty acids

Sewage sludge poses a serious environmental problem for large cities, and large amounts of materials in sludge, including organics, should be recovered rather than wasted. To achieve both sludge reduction and organic resource recovery, this study developed a new biorefinery technology that includes the hydrothermal treatment of sludge followed by fungal fermentation to form hyphae fibers and acidogenic fermentation to produce volatile fatty acids (VFAs). Hydrothermal treatment at 160 °C or 180 °C allows solubilization of approximately 40% of solid organics in sludge into the supernatant, resulting in significant sludge reduction and dewaterability improvement. The fermentation of the fungus Aspergillus niger converted waste organics in the hydrolyzed sludge liquor, with a chemical oxygen demand (COD) concentration of around 15,000 mg/L, into hyphae fibers, resulting in fungal biomass production of more than 1.7 g/L. After the recovery of hyphae fibers, the residual sludge liquor was further fermented to produce VFAs to a concentration of about 2500 mg COD/L. The genera Petrimonas, Arcobacter, and Aminobacterium played important roles in acidogenic fermentation. The stepped biorefinery strategy can transform approximately 35% of waste organics in the hydrothermal sludge liquor into valuable fibrous materials and VFAs for effective resource recovery.

Optimization of thermal hydrolysis process for enhancing anaerobic digestion in a wastewater treatment plant with existing primary sludge fermentation

Many wastewater treatment plants (WWTPs) adopted primary sludge fermentation to produce sludge liquor for the biological denitrification process. The fermented primary sludge (FPS) is usually co-digested with thickened waste activated sludge (TWAS) in the anaerobic digestion (AD) process. To date, there has been limited information on how the sludge thermal hydrolysis process (THP) could be retrofitted for enhancing AD in WWTPs with the existing primary sludge fermentation process. This study assessed two THP retrofitting schemes, (FPS + TWAS and TWAS alone) combining different exposure times (15, 30, and 60 min) and temperatures (140, 160, and 180 °C). The results suggested that temperature had more impact on sludge solubilization than exposure times. Notably, 180 °C was the most effective for sludge solubilization under both schemes. However, a higher degree of solubilization did not necessarily lead to higher methane yields. The THP of FPS + TWAS attained considerably higher methane yield than the pretreatment of TWAS alone.

Towards a bio-based circular economy in organic waste management and wastewater treatment – The Polish perspective

Bio-based solutions are expected to ensure technological circularity in priority areas such as agriculture, biotechnology, ecology, green industry or energy. Although Poland, unlike the other EU member states, has not yet adopted a precise political strategy to promote bioeconomy, it has taken several actions to enable smart, sustainable and inclusive growth. This goal can be achieved by developing selected bioeconomy-related areas such as the biogas industry together with novel technologies implemented to optimize treatment of municipal sewage and management of organic solid waste. Here, the relatively strong status of the Polish biogas sector is presented. The widely used practice of sewage sludge biomethanation has led to construction of numerous complex installations combining biological wastewater treatment plants with anaerobic digesters. Based on physico-chemical processing of biostabilized sludges, a novel method for efficient granulated soil fertilizer production is elaborated, in line with the concept of circular economy and the notion of “waste-to-product”. It is also shown that anaerobic fermentation of sewage sludges can be optimized by co-digestion with properly selected co-substrates to increase bioprocess yield and improve the resultant digestate fertilizer quality. The problem of post-fermentation eutrophic sludge liquors, environmentally hazardous waste effluents requiring proper treatment prior to discharge or field application, is addressed. Attempts to optimize biological treatment of digestate liquors with complex microbial consortia are presented. The Polish innovations described show that the “zero waste” path in circular bioeconomy may bring advantageous results in terms of transformation of waste materials into commercial, added-value products together with recovery of water resources.

Long-term simulation of a full-scale EBPR plant with a novel metabolic-ASM model and its use as a diagnostic tool

This study evaluates the predictive capacity of the META-ASM model, a new integrated metabolic activated sludge model, in describing the long-term performance of a full-scale enhanced biological phosphorus removal (EBPR) system that suffers from inconsistent performance. In order to elucidate the causes of EBPR upsets and troubleshoot the process accordingly, the META-ASM model was tested as an operational diagnostic tool in a 1336-day long-term dynamic simulation, while its performance was compared with the ASM-inCTRL model, a version based on the Barker & Dold model. Overall, the predictions obtained with the META-ASM without changing default parameters were more reliable and effective at describing the active biomass of polyphosphate accumulating organisms (PAOs) and the dynamics of their storage polymers. The primary causes of the EBPR upsets were the high aerobic hydraulic retention times (HRTs) and low organic loading rates (OLRs) of the plant, which led to periods of starvation. The impact of these factors on EBPR performance were only identified with the META-ASM model. Furthermore, the first signs of process upsets were predicted by variations in the aerobic PAO maintenance rates, suggesting that the META-ASM model has potential to provide an early warning of process upset. The simulation of a new viable operational strategy indicated that troubleshooting the process could be achieved by reducing the aerated volume by switching off air in the first half of the aeration tank. In this new strategy, the META-ASM model predicted a simultaneous improvement in the biological phosphorus (P) and nitrogen (N) removal due to the enhancement of the hydrolysis and fermentation of the mixed liquor sludge in the new unaerated zone, which increased the availability of volatile fatty acids (VFAs) for PAOs. This study demonstrates that the META-ASM model is a powerful operational diagnostic tool for EBPR systems, capable of predicting and mitigating upsets, optimising performance and evaluating new process designs.

Revealing the mechanisms for potassium ferrate affecting methane production from anaerobic digestion of waste activated sludge

This study investigated the issue of potassium ferrate (PF) affecting anaerobic methane generation from sludge by a set of experimental and model analyses. Experimental results indicated that the methane production was significantly promoted from 164.7 to 204.1 mL/g VSS (volatile suspended solids) with PF dosage enhanced from 0 to 0.05 g/g TSS (total suspended solids). Further enhancement of PF dosage reduced methane production, which even decreased to 135.4 mL/g VSS when PF dosage increased to 0.1 g/g TSS. Model-based analysis showed that except for methane production potential, the methane production rate was also promoted by PF treatment, which was sufficiently enhanced from 8.80 to 11.88 mL/g VSS/d when PF dosage was 0.05 g/g TSS. Mechanism studies indicated that PF not only promoted sludge disintegration, but also enhanced the proportion of biodegradable organics in sludge liquor, and the digestion potential of the non-biodegradable humus and lignocellulose were promoted.

Insights into thermal hydrolyzed sludge liquor - Identification of plant-growth-promoting compounds

This study proposes a new path to utilize thermal hydrolyzed sludge (TH sludge) as fertilizer given high value chemical compounds that can promote plant growth were identified in the liquid fraction of TH sludge (TH liquor). Together with micro- and macro-nutrients released/synthesized during thermal hydrolysis, the feasibility of using TH liquor as organic fertilizer was evaluated. Besides high contents of N, P and K, total free amino acids (FAAs) and plant-growth-promoting FAAs (including glutamic acid, leucine and cystine) also presented in high concentration (4.98–6.48 and 1.12–2.73 g/100 g) in the TH liquor. For the first time, phytohormone compound, indole-3-acetic acid, was observed and the content was the highest in TH liquor with 165 °C treatment (165 °C TH liquor). Meantime, 165 °C TH liquor did not have negative impact on the growth of soil microbes, and this product, instead, demonstrated stimulating effect on the plant growth. These results suggest that 165 °C TH liquor has a great potential to be an organic fertilizer. The remaining solids of TH sludge could be converted to valuable biochar. The holistic approach of using TH liquor as organic fertilizer and producing biochar could realize nearly zero-waste discharge in sludge management.