The study investigated the effects of long-chain fatty acids (LCFA) on anaerobic sludge treating lipid-rich wastewater. It involved batch experiments with three sludge samples: two acclimated to lipids and one non-acclimated. The experiments aimed to observe the degradation of LCFA, specifically oleate and palmitate, by dosing them at concentrations ranging from 50 to 600 mg/L. Measurements of the cumulative methane production and the LCFA concentration, quantified as fat, oil, and grease (FOG) were performed. To ensure the sludge was free from other biodegradable substrates, part of the samples was pre-incubated without feed. The tests were conducted with both pre-incubated and non-incubated inoculum sludge. The findings revealed that oleate was degraded more efficiently than palmitate across all sludge samples, with a greater conversion rate to methane. Sludge samples acclimated to lipids showed a superior capacity to degrade LCFA compared to non-acclimated ones. It was noted that at concentrations above 400 mg/L, the conversion of LCFAs to intermediate compounds was inhibited, although this did not affect the subsequent methane production. The study concludes with a recommendation for sludge adaptation strategies to boost the efficiency of anaerobic wastewater treatment systems dealing with lipid-rich waste. The presence of LCFA-degrading bacteria families like Kosmotogaceae, Petrotogaceae, and Synergistaceae in the acclimated sludge samples underscores the adaptation and potential for improved degradation performance.

To investigate the influence of high-pressure and shear effects introduced by a concentrated oxygen supply system on the membrane filtration performance, a laboratory-scale membrane bioreactor (MBR) fed artificial municipal wastewater was operated continuously for 80 days in four phases equipped with different aerations systems: (P1) bubble diffusers (days 0–40), (P2) concentrated oxygen supply system, the supersaturated dissolved oxygen (SDOX) (days 41–56), (P3) bubble diffusers (days 57–74), and (P4) SDOX (days 75–80). Various sludge physical-chemical parameters, visual inspection of the membrane, and permeability evaluations were performed. Results showed that the high-pressure effects contributed to fouling of the membranes compared to the bubble diffuser aeration system. Biofouling by microorganisms appeared to be the main contributor to the cake layer when bubble diffusers were used, while fouling by organic matter seemed to be the main contributor to the cake layer when SDOX was used. Small particle size distribution (PSD) (ranging from 1 to 10 and 1–50 μm in size) fractions are a main parameter affecting the intense fouling of membranes (e.g., formation of a dense and thin cake layer). However, PSD alone cannot explain the worsened membrane fouling tendency. Therefore, it can be assumed that a combination of several factors (which certainly includes PSD) led to the severe membrane fouling caused by the high-pressure and shear.

Thermal drying is an effective sludge treatment method for dealing with large volumes of sludge. Microwave (MW) technology has been proposed as an effective and efficient technology for sludge drying. The physical-chemical properties of the sludge depend both on the origin of the sludge, as well as on the treatment process at which the sludge has been exposed. The physical-chemical properties of the sludge affect the performance and the subsequent valorisation and management of the sludge. This study evaluated the effect of certain physical-chemical properties of the sludge (moisture content, organic content, calorific value, porosity, hydrophobicity, and water-sludge molecular interaction, among others) on the MW sludge drying and energy performance. Four different types of sludge were evaluated collected from municipal wastewater treatment plants and septic tanks. The performance of the MW system was assessed by evaluating the sludge drying rates, exposure times, energy efficiencies and power input consumed by the MW system and linking the MW drying performance to the sludge physical-chemical properties. The results confirmed that MW drying substantially extends the constant drying period associated with unbound water evaporation, irrespective of the sludge sample evaluated. However, the duration and intensity were determined to depend on the dielectric properties of the sludge, particularly on the distribution of bound and free water. Sludge samples with a higher amount of free and loosely bound water absorbed and converted MW energy into heat more efficiently than sludge samples with a lower amount of free water. As a result, the sludge drying rates increased and the constant drying rate period prolonged; hence, leading to an increase in MW drying energy efficiency. The availability of free and loosely bound water molecules was favoured when hydrophobic compounds, e.g., oils and fats, were present in the sludge.

The use of near-infrared (NIR) spectroscopy in wastewater treatment has continuously expanded. As an alternative to conventional analytical methods for monitoring constituents in wastewater treatment processes, the use of NIR spectroscopy is considered to be cost-effective and less time-consuming. NIR spectroscopy does not distort the measured sample in any way as no prior treatment is required, making it a waste-free technique. On the negative side, one has to be very well versed with chemometric techniques to interpret the results. In this study, filtered and centrifuged wastewater and sludge samples from a lab-scale membrane bioreactor (MBR) were analysed. Two analytical methods (conventional and NIR spectroscopy) were used to determine and compare major wastewater constituents. Particular attention was paid to soluble microbial products (SMPs) and extracellular polymeric substances (EPSs) known to promote membrane fouling. The parameters measured by NIR spectroscopy were analysed and processed with partial least squares regression (PLSR) and artificial neural networks (ANN) models to assess whether the evaluated wastewater constituents can be monitored by NIR spectroscopy. Very good results were obtained with PLSR models, except for the determination of SMP, making the model qualitative rather than quantitative for their monitoring. ANN showed better performance in terms of correlation of NIR spectra with all measured parameters, resulting in correlation coefficients higher than 0.97 for training, testing, and validation in most cases. Based on the results of this research, the combination of NIR spectra and chemometric modelling offers advantages over conventional analytical methods.

The provision of effective sanitation strategies has a significant impact on public health. However, the treatment of septic sludge still presents some challenges worldwide. Consequently, innovative technologies capable of an effective and efficient sludge treatment, mostly at a decentralized level, are in high demand to improve sanitation provision. To address this problem, this study evaluates a novel semi-decentralised mobile faecal sludge treatment system, the pilot-system for which consists of a combination of several individual processes including mechanical dewatering (MD), microwave (MW) drying, and membrane filtration (ultrafiltration [UF] and reverse osmosis [RO]). The system evaluation was carried out by treating raw, partially digested faecal sludge (FS) from septic tanks—hence, septic sludge (SS)—in the Jordan Valley, Jordan. The pilot-scale system exhibited an effective and flexible treatment performance for (i) sanitizing faecal sludge and related liquid streams (MW and UF); (ii) reducing the treated sludge mass (and sludge volume) (MD and MW); and (iii) producing a high-quality treated liquid stream ideal for water reclamation applications (UF and RO). The MD process removed approximately 99% of the initial SS water content. The MW drying system completely removed E. coli and dehydrated the dewatered sludge at low energy expenditures of 0.75 MJ kg⁻¹ and 5.5 MJ kg⁻¹, respectively. Such energy expenditures can be further reduced by approximately 40% by recovering energy in the condensate and burning the dried sludge, which can then be reused inland applications. The membrane filtration system (UF and RO) was able to produce high-quality treated water that is ideal for the water reuse applications that irrigation requires, as well as meeting the Jordanian standard 893/2006. In addition, the system can also be powered by renewable energy sources, such as photovoltaic energy. Therefore, this research demonstrates that the evaluated semi-decentralised mobile system is technically feasible for the in situ treatment of SS (sanitization and dehydration), while also being effective for simultaneously recovering valuable resources, such as energy, water, and nutrients.

The performance of a pulp mill wastewater treatment plant (WWTP) was assessed using the software BioWin aiming at providing alternatives for reducing even further the phosphorus (P) concentration in the treated effluent. The WWTP was designed without nutrient removal capacities, since pulp and paper wastewater is usually deficient in nutrients. However, the hard wood (Eucalyptus) which is processed in such plant has a higher P content compared to other types of woods, and part of that P ended up in the raw wastewater to be treated. The wastewater was characterized following the Dutch STOWA protocol. Once the model was calibrated, historical data from different periods of time was used to validate the model. The model was capable of describing the current plant operation, as well as its historical performance. Moreover, the model was used to evaluate different potential upgrading scenarios for the treatment plant aiming at increasing the plant performance on P removal. According to the model, the implementation of an anaerobic phase prior to the aerobic process showed to be a feasible scenario contributing to decrease the total phosphorus (TP) concentration in the treated effluent by approximately 58 %. In addition, applying chemical precipitation can further decrease the TP concentration below 0.1 mg/L. However, further research activities such as pilot-testing may be needed to validate the previous recommendations of applying enhance biological and chemical P removal at such pulp mill wastewater treatment plant.

The aerobic granular sludge (AGS) process is an effective wastewater treatment technology for organic matter and nutrient removal that has been introduced in the market rapidly. Until now, limited information is available on AGS regarding the removal of bacterial and viral pathogenic organisms present in sewage. This study focussed on determining the relation between reactor operational conditions (plug flow feeding, turbulent aeration and settling) and physical and biological mechanisms on removing two faecal surrogates, Escherichia coli and MS2 bacteriophages. Two AGS laboratory-scale systems were separately fed with influent spiked with 1.0 × 10⁶ CFU/100 mL of E. coli and 1.3 × 10⁸ PFU/100 mL of MS2 bacteriophages and followed during the different operational phases. The reactors contained only granular sludge and no flocculent sludge. Both systems showed reductions in the liquid phase of 0.3 Log₁₀ during anaerobic feeding caused by a dilution factor and attachment of the organisms on the granules. Higher removal efficiencies were achieved during aeration, approximately 1 Log₁₀ for E. coli and 0.6 Log₁₀ for the MS2 bacteriophages caused mainly by predation. The 18S sequencing analysis revealed high operational taxonomic units (OTUs) of free-living protozoa genera Rhogostoma and Telotrochidium concerning the whole eukaryotic community. Attached ciliates propagated after the addition of the E. coli, an active contribution of the genera Epistylis, Vorticella, and Pseudovorticella was found when the reactor reached stability. In contrast, no significant growth of predators occurred when spiking the system with MS2 bacteriophages, indicating a low contribution of protozoa on the phage removal. Settling did not contribute to the removal of the studied bacterial and viral surrogates.

Conventional diffused aeration systems (such as fine-bubble diffusers) exhibit a poor oxygen transfer in wastewater treatment plants (WWTPs), particularly when operating at sludge concentrations higher than 15 g L⁻¹. The supersaturated dissolved oxygen (SDOX) system has been proposed as an alternative for supplying dissolved oxygen (DO) at high mixed liquor suspended solids (MLSS) concentrations. The advantages introduced by such technology include the possibility of operating WWTPs at much higher than usual MLSS concentrations, increasing the treatment capacity of WWTPs. Recent studies have demonstrated that the SDOX system has higher oxygen transfer rates (OTRs) and oxygen transfer efficiencies (OTEs) relative to fine-bubble diffusers. However, it is unknown if the high-pressure conditions introduced by SDOX may possibly impact the biological performance of WWTPs. In this study, the effects of SDOX technology on the biological performance of a membrane bioreactor (MBR) were evaluated. The MBR was operated at an MLSS concentration of approximately 15 g L⁻¹ in four phases as follows: (P1) with bubble diffusers, (P2) with an SDOX unit, (P3) with the bubble diffusers, and (P4) with the SDOX unit. The performance of the MBR was assessed by monitoring the sludge concentration, as well as changes in the particle size distribution (PSD), sludge activity, organic matter removal and nitrification performance, and changes in the microbial community within the MBR. The operational conditions exerted by the SDOX technology did not affect the concentration of active biomass during the study period. The biological performance of the MBR was not affected by the introduction of the SDOX technology. Finally, the microbial community was relatively stable although some variations at the family and genus level were evident during each of the study phases. Therefore, the SDOX system can be proposed as an alternative technology for DO supply in WWTPs increasing the overall treatment capacity.

Oxygen transfer in wastewater treatment is significantly influenced by the mixed liquor suspended solids (MLSS). The effect is more pronounced at MLSS concentrations higher than 20 g L⁻¹ when supplying air by conventional diffused aeration systems. The oxygen transfer performance of a supersaturated oxygenation technology (i.e., the supersaturated dissolved oxygen (SDOX) system) was evaluated in clean water and in activated sludge with MLSS concentrations from 4 to 40 g L⁻¹ as a promising technology for uncapping such limitation. The evaluation was carried out at the laboratory facilities of the faculty of food technology and biotechnology at the University of Zagreb. The sludge was collected from a full-scale conventional activated sludge (CAS) wastewater treatment plant (WWTP) operated at a solid retention time (SRT) of approximately 5 days. The evaluation was carried out using a laboratory-scale setup consisting of a bench-scale SDOX system (2.75 L) supplying pure oxygen to a 5 L biological reactor. The SDOX exhibited oxygen mass transfer rate coefficient (K_La) values (2.6 h⁻¹) in clean water lower than for fine bubble diffusers (11 h⁻¹). However, higher oxygen transfer rate (OTR) values and alpha factors (mass transfer ratio of process-water to clean-water) as a function of the MLSS concentration were observed. A standard oxygen transfer efficiency (SOTE) of approximately 100 % in clean water was reported. The SDOX technology can be presented as a promising alternative for supplying dissolved oxygen (DO) into mixed liquor solutions; particularly, at the high MLSS concentrations required by high-loaded membrane bioreactor (HL-MBR) systems and aerobic digesters.

Using a mathematical model, a resource recovery assessment was carried out at a pulp mill activated sludge wastewater treatment plant (WWTP) located in Uruguay. Through the evaluation of different scenarios, the potential production of methane from secondary sludge, with its inherent energy savings, and the recovery of phosphorus (P) as struvite were estimated. Considering the current WWTP configuration with a sludge retention time (SRT) of 32 days, and according to the model, which is a simplification of reality, the assessment indicates that the implementation of an anaerobic digester (AD) to treat the excess sludge can lead to a methane production of approximately 1736 m³ CH₄ d⁻¹, being a promising alternative to increase the WWTP treatment performance. Furthermore, the model predictions suggest that by shortening the SRT from 32 to 5 days, the methane production could increase by up to 5568 m³ CH₄ d⁻¹. If the methane produced is used to generate electrical energy to operate the WWTP, energy savings of about 88% can be achieved. Regarding the potential recovery of P as struvite, the addition of a struvite reactor could be an efficient option to recover approximately 1611 mg L⁻¹ of struvite (corresponding to a load of about 433 kg d⁻¹). By optimizing the process performance, these findings highlight the potential recovery of resources in pulp mill WWTP, while complying with stringent effluent discharge standards. In addition, further research activities such as pilot-test or detailed laboratory studies may be needed to validate the previous recommendations for industrial scale application.

Sewage sludge management and treatment can represent up to approximately 30% of the overall operational costs of a wastewater treatment plant. Microwave (MW) drying has been recognized as a feasible technology for sludge treatment. However, MW drying systems exhibit high energy expenditures due to: (i) unnecessary heating of the cavity and other components of the system, (ii) ineffective extraction of the condensate from the irradiation cavity, and (iii) an inefficient use of the microwave energy, among others issues. This study investigated the performance of a novel pilot-scale MW system for sludge drying, specifically designed addressing the shortcomings previously described. The performance of the system was assessed drying municipal centrifuged wasted activated sludge at MW output powers from 1 to 6 kW and evaluating the system's drying rates and exposure times, specific energy outputs, MW generation efficiencies, overall energy efficiencies, and specific energy consumption. The results indicated that MW drying significantly extends the duration of the constant rate drying period associated with the evaporation of the unbound sludge water, a phase associated with low energy input requirement for evaporating water. Moreover, the higher the MW output power, the higher the sludge power absorption density, and the MW generation efficiency. MW generation efficiencies of up to 70% were reported. The higher the power absorption density, the lower the chances for energy losses in the form of reflected power and/or energy dissipated into the MW system. Specific energy consumptions as low as 2.6 MJ L⁻¹ (0.74 kWh L⁻¹) could be achieved, well in the range of conventional thermal dryers. The results obtained in this research provide sufficient evidence to conclude that the modifications introduced to the novel pilot-scale MW system mitigated the shortcomings of existing MW systems, and that the technology has great potential to effectively and efficiently drying municipal sewage sludge.

The aim of this study was to evaluate the effectiveness of the novel aerobic granular sludge (AGS) wastewater treatment technology in removing faecal indicator organisms (FIOs) compared to the conventional activated sludge (CAS) treatment system. The work was carried out at two full-scale wastewater treatment plants (WWTP) in the Netherlands, Vroomshoop and Garmerwolde. Both treatment plants have a CAS and AGS system operated in parallel. The parallel treatment lines are provided with the same influent wastewater. The concentrations of the measured FIOs in the influent of the two WWTPs were comparable with reported literature values as follows: F-specific RNA bacteriophages at 10⁶ PFU/100 mL, and Escherichia coli (E. coli), Enterococci, and Thermotolerant coliforms (TtC) at 10⁵ to 10⁶ CFU/100 mL. Although both systems (CAS and AGS) are different in terms of design, operation, and microbial community, both systems showed similar FIOs removal efficiency. At the Vroomshoop WWTP, Log₁₀ removals for F-specific RNA bacteriophages of 1.4 ± 0.5 and 1.3 ± 0.6 were obtained for the AGS and CAS systems, while at the Garmerwolde WWTP, Log₁₀ removals for F-specific RNA bacteriophages of 1.9 ± 0.7 and 2.1 ± 0.7 were found for the AGS and CAS systems. Correspondingly, E. coli, Enterococci, and TtC Log₁₀ removals of 1.7 ± 0.7 and 1.1 ± 0.7 were achieved for the AGS and CAS systems at Vroomshoop WWTP. For Garmerwolde WWTP Log₁₀ removals of 2.3 ± 0.8 and 1.9 ± 0.7 for the AGS and CAS systems were found, respectively. The measured difference in removal rates between the plants was not significant. Physicochemical water quality parameters, such as the concentrations of organic matter, nutrients, and total suspended solids (TSS) were also determined. Overall, it was not possible to establish a direct correlation between the physicochemical parameters and the removal of FIOs for any of the treatment systems (CAS and AGS). Only the removal of TSS could be positively correlated to the E. coli removal for the AGS technology at the evaluated WWTPs.

The co-treatment of two synthetic faecal sludges (FS-1 and FS-2) with municipal synthetic wastewater (WW) was evaluated in an aerobic granular sludge (AGS) reactor. After characterisation, FS-1 showed the following concentrations, representative for medium-strength FS: 12,180 mg TSS L⁻¹, 24,300 mg total COD L⁻¹, 93.8 mg PO₃-P L⁻¹, and 325 mg NH₄-N L⁻¹. The NO₃-N concentration was relatively high (300 mg L⁻¹). For FS-2, the main difference with FS-1 was a lower nitrate concentration (18 mg L⁻¹). The recipes were added consecutively, together with the WW, to an AGS reactor. In the case of FS-1, the system was fed with 7.2 kg total COD m⁻³d⁻¹ and 0.5 kg Nitrogen m⁻³d⁻¹. Undesired denitrification occurred during feeding and settling resulting in floating sludge and wash-out. In the case of FS-2, the system was fed with 8.0 kg total COD m⁻³d⁻¹ and 0.3 kg Nitrogen m⁻³d⁻¹. The lower NO₃-N concentration in FS-2 resulted in less floating sludge, a more stabilised granular bed and better effluent concentrations. To enhance the hydrolysis of the slowly biodegradable particulates from the synthetic FS, an anaerobic stand-by period was added and the aeration period was increased. Overall, when compared to a control AGS reactor, a lower COD consumption (from 87 to 35 mg g⁻¹ VSS h⁻¹), P-uptake rates (from 6.0 to 2.0 mg P g VSS⁻¹ h⁻¹) and NH₄-N removal (from 2.5 to 1.4 mg NH₄-N g VSS⁻¹ h⁻¹) were registered after introducing the synthetic FS. Approximately 40% of the granular bed became flocculent at the end of the study, and a reduction of the granular size accompanied by higher solids accumulation in the reactor was observed. A considerable protozoa Vorticella spp. bloom attached to the granules and the accumulated particles occurred; potentially contributing to the removal of the suspended solids which were part of the FS recipe.

In this study, the impact of applied solids retention time (SRT) on the biological performance of an anaerobic membrane bioreactor (AnMBR) treating synthetic dairy wastewater with high lipid content was assessed. Two side-stream AnMBR systems were operated at an SRT of 20 and 40 days (R20 and R40, respectively), equipped with an inside-out tubular membrane operated in cross-flow mode under full-scale operational conditions, i.e. crossflow velocity, transmembrane pressure, membrane flux. Successful operation was achieved and removal efficiencies of both reactors were up to 99% applying an organic loading rate (OLR) of 4.7 g COD L⁻¹ d⁻¹. No precipitation of lipids was observed throughout the operational period, keeping the lipids available for the anaerobic degradation. Long chain fatty acid (LCFA) accumulation was very modest and amounted 148 and 115 mg LCFA-COD per gram of volatile suspended solids (VSS) for R20 and R40, respectively. At an SRT of 40 days, a slightly better biological conversion was obtained. Periodically performed specific methanogenic activity (SMA) tests showed stabilization of the SMA for R40 sludge, whereas for R20 sludge the SMA continued to decrease. This study revealed a more stable reactor performance operating the AnMBR at an SRT of 40 days compared to 20 days.

The operation of membrane bioreactors (MBRs) at higher than usual mixed liquor suspended solids (MLSS) concentrations may enhance the loading rate treatment capacity while minimizing even further the system’s footprint. This requires operating the MBR at the highest possible MLSS concentration and biomass activity (e.g., at high loading rates and low solid retention times (SRTs)). Both a negative effect of the MLSS concentrations and a positive effect of the SRT on the oxygen transfer have been reported when using conventional fine bubble diffusers. However, most of the evaluations have been carried out either at extremely high SRTs or at low MLSS concentrations eventually underestimating the effects of the MLSS concentration on the oxygen transfer. This research evaluated the current limitations imposed by fine bubble diffusers in the context of the high-loaded MBR (HL-MBR) (i.e., high MLSS and short SRT—the latter emulated by concentrating municipal sludge from a wastewater treatment plant (WWTP) operated at a short SRT of approximately 5 days). The high MLSS concentrations and the short SRT of the original municipal sludge induced a large fraction of mixed liquor volatile suspended solids (MLVSS) in the sludge, promoting a large amount of sludge flocs that eventually accumulated on the surface of the bubbles and reduced the free water content of the suspension. Moreover, the short SRTs at which the original municipal sludge was obtained eventually appear to have promoted the accumulation of surfactants in the sludge mixture. This combination exhibited a detrimental effect on the oxygen transfer. Fine bubble diffusers limit the maximum MLSS concentration for a HL-MBR at 30 g L ⁻¹ ; beyond that point is either not technically or not economically feasible to operate; an optimum MLSS concentration of 20 g L ⁻¹ is suggested to maximize the treatment capacity while minimizing the system’s footprint.