Wastewater Flow Research Articles

A Review of Computational Modeling in Wastewater Treatment Processes.

Wastewater treatment companies are facing several challenges related to the optimization of energy efficiency, meeting more restricted water quality standards, and resource recovery potential. Over the past decades, computational models have gained recognition as effective tools for addressing some of these challenges, contributing to the economic and operational efficiencies of wastewater treatment plants (WWTPs). To predict the performance of WWTPs, numerous deterministic, stochastic, and time series-based models have been developed. Mechanistic models, incorporating physical and empirical knowledge, are dominant as predictive models. However, these models represent a simplification of reality, resulting in model structure uncertainty and a constant need for calibration. With the increasing amount of available data, data-driven models are becoming more attractive. The implementation of predictive models can revolutionize the way companies manage WWTPs by permitting the development of digital twins for process simulation in (near) real-time. In data-driven models, the structure is not explicitly specified but is instead determined by searching for relationships in the available data. Thus, the main objective of the present review is to discuss the implementation of machine learning models for the prediction of WWTP effluent characteristics and wastewater inflows as well as anomaly detection studies and energy consumption optimization in WWTPs. Furthermore, an overview considering the merging of both mechanistic and machine learning models resulting in hybrid models is presented as a promising approach. A critical assessment of the main gaps and future directions on the implementation of mathematical modeling in wastewater treatment processes is also presented, focusing on topics such as the explainability of data-driven models and the use of Transfer Learning processes.

Current Plastic Waste Status and Its Leakage at Tam Giang–Cau Hai Lagoon System in Central Vietnam

Plastic waste poses a significant threat to the environment, impacting both aquatic ecosystems and human health. This study aimed to quantify the leakage of plastic waste from urban and rural areas into the Tam Giang–Cau Hai lagoon system area in Vietnam. The research involved conducting surveys and sampling plastic waste in wards and communes surrounding the Tam Giang–Cau Hai lagoon system, as well as utilizing a waste flow diagram to calculate the amount of plastic waste leakage into the environment. The findings of the study reveal that the annual plastic leakage in this study area is approximately 479 tons. The majority of this waste enters the water body system, accounting for 74.1% of the total leakage, followed by land areas at 23.4% and land burning at 2.5%. Among the sources contributing to the wastewater flow in the area, households and markets were found to be the two primary contributors. Household waste accounted for 70.4% (2806 tons year−1) of the total, while the market sources accounted for 16.9% (675 tons year−1). This study marks the inaugural effort to assess the extent of plastic waste released from Hue City into the Tam Giang–Cau Hai lagoon system. It plays a pivotal role in examining the makeup, source of plastic waste and path of plastic waste leakage.

Preparation of Fe/Zr bimetallic oxide beads and its performance and mechanism for advanced treatment of actual phosphorus-containing wastewater

Phosphorus removal by adsorption method has unique advantages in the wastewater treatment. The granulation and recycling performance of adsorbent are key factors restricting its practical application. To solve these problems, this study used an environmentally friendly binder to prepare Fe/Zr bimetallic oxide beads (Fe/Zr-Bead) with high mechanical strength and recyclability. The batch experiment results confirmed that the maximum adsorption capacity of Fe/Zr-Bead was 24.60 mg/g. During extended operational trials, the Fe/Zr-Bead-filled fixed-bed column enables unhindered flow of wastewater without blockages, effectively treating simulated wastewater with varying initial concentrations of phosphorus. Furthermore, Fe/Zr-Bead exhibits prominent performance in the treatment of real wastewater plant effluent, reducing the initial phosphorus concentration from 0.416 mg/L to below 0.05 mg/L. Even after undergoing 11 cycles of adsorption and desorption, the phosphorus removal capacity of Fe/Zr-Bead only decreased by 5.5 %. Moreover, the desorption solution, which contains phosphorus, can reach up to 57.93 mg/L, making it suitable for phosphorus resource recovery. Ligand exchange between hydroxyl oxygen and phosphorus was found the main mechanism for phosphorus removal by Fe/Zr-Bead. This study is valuable for overcoming the limitations of adsorption materials in practical applications and also provide practical and technical support for advancing phosphorus treatment in the future.

Assessing the potential application of bacteria-based self-healing cementitious materials for enhancing durability of wastewater treatment infrastructure

Wastewater treatment plants (WWTPs) around the world are mainly built using concrete. The continuous exposure to wastewater affects the durability of concrete structures and requires costly maintenance or replacement. Concrete production and repair represents ∼8% of the global anthropogenic CO2 emissions due to the use of cement, thus contributing to climate change. Developing a more sustainable cementitious material is therefore required for this vital health infrastructure. In this study, the feasibility of using bacteria-based self-healing (BBSH) cementitious materials for WWTPs is assessed by exposing BBSH mortar prisms to a continuous municipal wastewater flow and comparing their self-healing capacity to equivalent mortar prisms exposed to tap water. Microscopy imaging, water-flow tests and micro-CT analyses were performed to evaluate the self-healing efficiency of the mortar prisms, while SEM-EDX and Raman spectroscopy were used to characterise the healing products. Our work represents the first systematic study of the healing potential of BBSH in mortar exposed to wastewater. The results indicate that the purposely added bacteria are able to induce calcium carbonate precipitation when exposed to wastewater conditions. Moreover, if additional sources of calcium and carbon are embedded within the cement matrix, the rich bacterial community inherently present in the wastewater is capable of inducing calcium carbonate precipitation, even if no bacteria are purposely added to the mortar. The results of this study offer promising avenues for the construction of more sustainable wastewater infrastructure, with the potential of significantly reducing costs and simplifying the production process of BBSH concretes for this specific application.

Anthropogenic activities significantly increase annual greenhouse gas (GHG) fluxes from temperate headwater streams in Germany

Abstract. Anthropogenic activities increase the contributions of inland waters to global greenhouse gas (GHG; CO2, CH4, and N2O) budgets, yet the mechanisms driving these increases are still not well constrained. In this study, we quantified year-long GHG concentrations, fluxes, and water physico-chemical variables from 28 sites contrasted by land use across five headwater catchments in Germany. Based on linear mixed-effects models, we showed that land use was more significant than seasonality in controlling the intra-annual variability of the GHGs. Streams in agriculture-dominated catchments or with wastewater inflows had up to 10 times higher daily CO2, CH4, and N2O emissions and were also more temporally variable (CV > 55 %) than forested streams. Our findings also suggested that nutrient, labile carbon, and dissolved GHG inputs from the agricultural and settlement areas may have supported these hotspots and hot-moments of fluvial GHG emissions. Overall, the annual emission from anthropogenic-influenced streams in CO2 equivalents was up to 20 times higher (∼ 71 kg CO2 m−2 yr−1) than from natural streams (∼ 3 kg CO2 m−2 yr−1), with CO2 accounting for up to 81 % of these annual emissions, while N2O and CH4 accounted for up to 18 % and 7 %, respectively. The positive influence of anthropogenic activities on fluvial GHG emissions also resulted in a breakdown of the expected declining trends of fluvial GHG emissions with stream size. Therefore, future studies should focus on anthropogenically perturbed streams, as their GHG emissions are much more variable in space and time and can potentially introduce the largest uncertainties to fluvial GHG estimates.

Which Configuration of Photocatalytic Membrane Reactors Has a Major Potential to Be Used at an Industrial Level in Tertiary Sewage Wastewater Treatment?

Photocatalytic membrane reactors (PMRs) have been found to be very effective in the removal of organic pollutants (particularly recalcitrant compounds) from wastewater because they allow for the mineralization of organic pollutants to innocuous by-products, thus achieving high-quality treated water. Owing to the very high volumes of water involved, treated sewage wastewater could be reused if a very efficient tertiary stage, like a PMR, can be foreseen. In this review, the two main PMR configurations (photocatalytic membranes and slurry PMRs) were analyzed as requirements of a tertiary treatment of sewage wastewater considering six design and operational parameters of such plants: (i) continuous wastewater flow rate from the secondary stage; (ii) the self-control of the photodegradation rate related to wastewater chemical–physical parameters; (iii) ability to handle variations of wastewater concentration and flow rate; (iv) the control of the quality of treated wastewater; (v) low plant footprint; and (vi) easy maintenance. In this analysis, some characteristics of photocatalysis (which involves three phases: solid (the photocatalyst), liquid (the wastewater), and gas (oxygen or air)) and those of membranes (they can be produced using different materials and configurations, different processes (pressure-driven or not pressure-driven), etc.) were considered. The obtained results show that slurry PMRs seem more suitable than photocatalytic membranes for such applications. We believe this review can trigger a shift in research from the laboratory to industry in using photocatalytic membrane reactors.

Feasibility of bio-filter in treating low strength nitrogen wastewater under adverse temperatures

As a promising nitrogen removal technology, anammox still faces the bottlenecks of low temperatures, low substrates, and large wastewater flow in mainstream. This study investigated the feasibility of anammox bio-filter (A-BF) as advanced nitrogen removal unit for sewage treatment in low temperature climates. Results showed when treating 7 mg-NH4+-N·L−1 and 10 mg-NO2--N·L−1 wastewater, A-BF achieved 71.8 ± 5.6 % and 60.10 ± 10.31 % of total nitrogen removal efficiency (TNRE) under nitrogen loading rate (NLR) of 1.20 ± 0.30 kg-N m−3 d−1, within 0.3 h at 25 and 7.5 °C, respectively, based on ＜8 mg L−1 effluent. Further analysis showed that A-BF performance was recovered with TNRE of 71.8 ± 5.6 % when back to 25 °C after collapsing with TNRE of 24.30 ± 15.73 % at 5 °C. Dominant Candidatus Brocadia in anammox bacteria (AnAOB) (3.59–6.24 %) contributed to higher 0.22 and 0.46 g-N·g-VSS−1·d−1 biomass activity at 25 °C. This study provided possible and low-carbon strategy for advanced nitrogen removal.

Meandering Flow Filter for Phosphorus Removal as a Component of Small Wastewater Treatment Plants—A Case Study

Chemical phosphorus removal in wastewater treatment plants can be carried out by precipitation with iron or aluminum salts or by filtering wastewater through a bed of active sorptive material. This work aimed to investigate whether using a meander flow filter filled with the sorption material Rockfos® would improve phosphorus removal efficiency in a selected wastewater treatment plant. Tests were performed under laboratory conditions using a model of a meander flow filter and a similar filter under field conditions at full technical scale. This filter was the final element of a hybrid constructed wetland located in the village of Białka in the municipality of Dębowa Kłoda in southeastern Poland. A laboratory model of a phosphorus removal filter with vertical incomplete baffles forcing a meandering water flow was constructed to determine the hydraulic conditions of the flow. After one year of operation, the filter with horizontal wastewater flow operating at its full technical scale (without meanders) was modified by inserting appropriate baffles that were analogous to those in the laboratory model. The analysis of the hydraulic conditions in the laboratory model showed that, under the assumed conditions, wastewater flows through the filter layer in a laminar motion, so such filters can be modeled using the Kozeny–Carman formula. It was shown that, after approximately a year of operation in a filter operating at full technical scale, before modification, dead spaces formed, thus causing the channel and primarily surface flow of wastewater. The phosphorus removal efficiency during this test period averaged 9.4%. After introducing baffles and forcing meander flow in the filter chamber, the efficiency increased to 40.6%. The results indicate that meander flow filters can improve phosphorus removal efficiency in small wastewater treatment plants.

Pharmaceutical residues in the ecosystem: Antibiotic resistance, health impacts, and removal techniques

Hospital wastewater has emerged as a major category of environmental pollutants over the past two decades, but its prevalence in freshwater is less well documented than other types of contaminants. Due to compound complexity and improper operations, conventional treatment is unable to remove pharmaceuticals from hospital wastewater. Advanced treatment technologies may eliminate pharmaceuticals, but there are still concerns about cost and energy use. There should be a legal and regulatory framework in place to control the flow of hospital wastewater. Here, we review the latest scientific knowledge regarding effective pharmaceutical cleanup strategies and treatment procedures to achieve that goal. Successful treatment techniques are also highlighted, such as pre-treatment or on-site facilities that control hospital wastewater where it is used in hospitals. Due to the prioritization, the regulatory agencies will be able to assess and monitor the concentration of pharmaceutical residues in groundwater, surface water, and drinking water. Based on the data obtained, the conventional WWTPs remove 10–60% of pharmaceutical residues. However, most PhACs are eliminated during the secondary or advanced therapy stages, and an overall elimination rate higher than 90% can be achieved. This review also highlights and compares the suitability of currently used treatment technologies and identifies the merits and demerits of each technology to upgrade the system to tackle future challenges. For this reason, pharmaceutical compound rankings in regulatory agencies should be the subject of prospective studies.

Sedimentation in heavy laden urban combined sewer conduits using a multi-phase Eulerian-Eulerian model

ABSTRACT To investigate the sedimentation through urban wastewater pipelines a semicircular polyethylene pipeline of diameter 0.40 m and length 18 m in nearly horizontal orientation with a longitudinal slope of 0.01 for a discharge capacity of 0.0147 m3/s and a volumetric flow concentration of 30% has been used. The solid phase consists of three different particle sizes i.e. 0.25 × 10−3m, 0.35 × 10−3 m and 0.50 × 10−3m with the greatest frequency in the wastewater flow being a density of 2650 kg/m3. The flow has been simulated by Ansys-Fluent (2020) software. The effects of particle size on various slurry flow parameters such as pressure drop, solid phase velocity distribution, friction factor, granular pressure, turbulent viscosity, turbulent kinetic energy and its dissipation all have been analyzed. The location of maximum deposition is also determined and it occurred at x/R = 77.5. Finally, a relationship between the thickness of sedimentation and volume concentration has been proposed.

Time series modelling for wastewater-based epidemiology of COVID-19: A nationwide study in 40 wastewater treatment plants of Belgium, February 2021 to June 2022

BackgroundWastewater-based epidemiology (WBE) has been implemented to monitor surges of COVID-19. Yet, multiple factors impede the usefulness of WBE and quantitative adjustment may be required. AimWe aimed to model the relationship between WBE data and incident COVID-19 cases, while adjusting for confounders and autocorrelation. MethodsThis nationwide WBE study includes data from 40 wastewater treatment plants (WWTPs) in Belgium (02/2021–06/2022). We applied ARIMA-based modelling to assess the effect of daily flow rate, pepper mild mottle virus (PMMoV) concentration, a measure of human faeces in wastewater, and variants (alpha, delta, and omicron strains) on SARS-CoV-2 RNA levels in wastewater. Secondly, adjusted WBE metrics at different lag times were used to predict incident COVID-19 cases. Model selection was based on AICc minimization. ResultsIn 33/40 WWTPs, RNA levels were best explained by incident cases, flow rate, and PMMoV. Flow rate and PMMoV were associated with −13.0 % (95 % prediction interval: −26.1 to +0.2 %) and +13.0 % (95 % prediction interval: +5.1 to +21.0 %) change in RNA levels per SD increase, respectively. In 38/40 WWTPs, variants did not explain variability in RNA levels independent of cases. Furthermore, our study shows that RNA levels can lead incident cases by at least one week in 15/40 WWTPs. The median population size of leading WWTPs was 85.1 % larger than that of non‑leading WWTPs. In 17/40 WWTPs, however, RNA levels did not lead or explain incident cases in addition to autocorrelation. ConclusionThis study provides quantitative insights into key determinants of WBE, including the effects of wastewater flow rate, PMMoV, and variants. Substantial inter-WWTP variability was observed in terms of explaining incident cases. These findings are of practical importance to WBE practitioners and show that the early-warning potential of WBE is WWTP-specific and needs validation.

Additional Treatment of Nitrogen and Phosphorus Using Natural Materials in Small-Scale Domestic Wastewater Treatment Unit

The conventional wastewater treatment methods only remove up to 80% of total nitrogen (N) or phosphorus (P) from wastewater, so additional facilities are needed. This article describes a newly created other wastewater treatment unit (NCU) that increases the effectiveness of P and N removal of the small-scale biological wastewater treatment plant. This work aims to evaluate the capacity of simultaneous elimination from wastewater nitrogen (NH4-N, NO3-N) and phosphorus (PO4-P) by adsorption. NCU was filled with the sorbent material zeolite (clinoptilolite) and OCS (Fe, Mn, Ca oxides coated sand). After treatment in the main plant, wastewater flows through the NCU without using electric power. A compact system consisting of a main treatment plant and the NCU worked for 4 months, as the harmonized European Standard EN 12566-7 recommended. The NCU unit reduced PO4-P, NH4-N, and NO3-N concentrations in the effluent (74–98%, 52–99%, and 50–98%, respectively). In general, the small-scale system treated wastewater did not contain more than 1 mg/L phosphorus concentration and not more than 10 mg/L nitrogen concentration. This study demonstrates that treatment in NCU is an ecological and environmentally friendly method suitable for decentralized wastewater treatment.

In situ immobilization of δ-MnO2 nanosheets on a porous support for rapid and continuous cleaning of bisphenol A-spiked water

Bisphenol A (BPA), a building block of various plastics, is invading biosystems through drinking water and raising concerns about their adverse impacts on human health. Filtration, biological, and oxidation methods have been developed to decontaminate BPA, but high energy demand or lengthy biodegradation process acts as limiting factors. Recently, δ-MnO2 with layered structure has emerged as a promising tool for BPA degradation. However, the reaction rate of BPA degradation suffers from the nature of aggregation in free-standing δ-MnO2 nanosheets with limited accessible active sites towards BPA. To overcome this critical challenge, this study demonstrates that the immobilization of δ-MnO2 nanosheets on a porous support can enhance BPA degradation rate due to the increased exposure of active sites of δ-MnO2. As a result, the δ-MnO2 nanosheets immobilized on porous diatom particles via polydopamine (PDA) binder degrades BPA (k’ ∼0.774 L g−1 min−1) 14 times faster than free-standing δ-MnO2 (k’ ∼0.056 L g−1 min−1). Furthermore, the resulting δ-MnO2-PDA-diatom degrades ∼ 99 % of BPA within 20 min and can be recycled without any performance loss up to 7 times, providing the reusability towards BPA removal in a sustainable and eco-friendly manner. More importantly, the degraded products of BPA resulting from radical transfers, coupling, and fragmentation reactions do not cause any estrogenic response or toxicity to ecological systems, as examined with human and fish cells. Finally, a column packed with δ-MnO2-PDA-diatom demonstrates 99 % BPA removal with continuous flows of BPA-spiked wastewater. We propose that this advanced system will be readily extended to remove a broad array of water contaminants that will disrupt the physiological function of organs and their roles in the endocrine cross-talk between the reproductive hormones.

Desain Perencanaan Instalasi Pengolahan Air Limbah Domestik

This research aims to understand the existing condition of domestic wastewater treatment at Pondok Pesantren Attabiyatussakilah Kendari. It aims to identify the characteristics of wastewater generated at Pondok Pesantren Attabiyatussakilah Kendari. It also aims to design a domestic wastewater treatment installation for Pondok Pesantren Attabiyatussakilah Kendari. The methods used in this research are quantitative, qualitative, and experimental. The research findings indicate that the existing domestic wastewater treatment installation at Pondok Pesantren Attabiyatussakilah Kendari is currently absent. Generally, the wastewater is discharged into the drainage system without undergoing any treatment process. The calculated wastewater flow rate is 19.75 m3/day. The planned dimensions of the wastewater treatment plant (IPAL) consist of a sedimentation tank (settler) with dimensions of 3.35 m × 3.30 m × 3.54 m and an Anaerobic Filter (AF) tank with dimensions of 1 m × 3.32 m × 2.40 m.

Using wastewater-based epidemiology to evaluate the relative scale of use of opioids

Wastewater analysis (WWA) has been used as a tool to monitor population drug use, both pharmaceutical and illicit, for over 15 years. Policymakers, law enforcement and treatment services may use WWA-derived data to seek an objective understanding of the extent of drug use in specific areas. Therefore, wastewater data should best be reported in a meaningful form to allow those that are not experts in the field to compare the scale within and between drug classes. Excreted drug loads quantified in wastewater describe the mass of drug present in the sewer. Normalisation for wastewater flow and population is standard practice and critical for comparing drug loads between different catchments and indicates a transition to an epidemiological approach (wastewater-based epidemiology (WBE)). A further consideration is necessary to accurately compare the measured level of one drug to another. The standard dose of a drug taken to elicit a therapeutic effect will vary, with some compounds requiring microgram amounts, while others are administered in the gram range. When WBE data is expressed with units representing excreted or consumed loads without considering dose amounts, the scale of drug use when comparing multiple compounds becomes distorted. To demonstrate the utility and significance of including known excretion rates, potency and typical dose amounts into back-calculations of the measured drug load, this paper compares the levels of 5 prescribed (codeine, morphine, oxycodone, fentanyl and methadone) and 1 illicit (heroin) opioid from South Australian wastewater. The data is presented at each stage of the back-calculation starting with the total mass load measured, to consumed amounts factoring in excretion rates and finally the number of doses the load equates to. This is the first paper to describe the levels of 6 opioids measured in wastewater over a 4-year period in South Australia that demonstrate the relative scale of use.

Hospitals and households as primary emission sources for risk-posing pharmaceuticals in municipal wastewater

A wide range of pharmaceutical residues is known to occur in the environment. While they are released into surface waters mainly through centralized wastewater treatment plants (WWTPs), their primary emission sources are located upstream in the sewer network. Information on emissions from different types of primary emission sources is scarce. However, such information could help direct emission reduction measures more efficiently. In this study, we analysed the concentrations of selected active pharmaceutical ingredients (APIs) in wastewater samples taken from altogether ten sites, covering primary emission sources (hospitals and households), and conventional WWTPs. The concentrations in WWTP effluents were used to identify APIs causing risk in recipient waterbodies. Furthermore, the API loads from households and hospitals were compared to those reaching the WWTP in mixed influents. Our results confirm previously published observations of several pharmaceuticals exceeding their predicted no-effect concentrations in effluent wastewaters. Moreover, the concentrations of most of the analysed APIs are comparatively high in hospital wastewaters, resulting in elevated risk quotients. While the total API loads are relatively low from primary emission sources, owing to the low wastewater volume generated at those sites, per capita emissions were shown to be several times higher at hospital sites than at household sites for APIs such as metronidazole, trimethoprim, and ofloxacin. These findings indicate, that directing emission reduction measures to hospitals could be an effective way to decrease the loads of several risk-posing APIs into the environment, especially where hospital contribution to overall wastewater flow to WWTPs is high.

Enhancement of a Decentralized Wastewater Treatment System by Applying a Bio-tower - A Project for Improving our Environmental Footprint

To investigate if decentralized wastewater treatment systems impact on the environment performance can be improved, a Field Bio-tower Tank Septic system was designed, installed on an existing 1,500-gal (5678 l) decentralized wastewater treatment system. The system was started up during a 14-day start-up phase, followed by a 130-day test phase. The system was operated at an average hydraulic retention time of 16.7 days based on a 90 gal (204.4 l) daily influent wastewater flow.
 The systems recirculation flow for the bio-tower was 22.6 l/min (6 gal/min) for the start-up phase and 40.0 l/min (10.6 gal/min) for the test period with a corresponding recirculation of the entire septic tank from 5.7 to 10.1 times a day respectively.
 During the testing period a daily average temperature of 19.3°C (66.7°F) and an average rainfall of 5 l/m² was observed. The FBST system operated at an average influent pH level and temperature of 8.6 and 22.0°C. The average effluent pH and temperature was 8.5 of 20.9°C.
 The installed system reduced on average the influent TS from 79151 mg/l to 43021 mg/l and showed an average reduction of the TDS from 36424 mg/l to 21965 mf/l. The TSS and VSS was reduced on average from 94.1 mg/l to 69.9 mg/l and 89.0 mg/l to 64.9 mg/l.
 NH3-N content was reduced from 57.5 mg/l in the influent to 53.4 mg/l in the effluent. The average BOD and COD was reduced from the average influent value of 88.2 mg/l and 318.2 mg/l to 66.8 mg/l and 256.2 mg/l respectively. However, at the end of the 130-day test period BOD and COD values were the lowest at 15.5 mg/l and 56.0 mg/l respectively, indicating bacteria cultures are well established and the system operation of the FBTS system is mostly constant.
 This research showed that the FBST system can improve operations of a DWWTS system significantly reducing the effluent load over 10 times compared to the influent load of the system.

Influence of loading rates and feeding conditions on hybrid constructed wetlands integrated with microbial fuel cells

The present study had as objective to evaluate the influence of different operation conditions on two treatment systems composed of anerobic biofilter (AF) and hybrid constructed wetlands (CWs). Both treatment lines had as the first treatment stages an 1450 L AF unit and a CW designed as a Floating Treatment Wetland. Then, a pump directed half of the wastewater flow for each of the treatment lines. One of the lines was composed of a Vertical Flow CW incorporated with microbial fuel cells (CW-MFC), called Configuration 1 (C1), whereas the other line consisted of a Vertical Flow CW (VFCW) and a Horizontal Flow CW (HFCW), named Configuration 2 (C2). The treatment system was fed with wastewater generated in a university campus and monitored for 13 months, with three operation conditions tested: 3 pulses per day with 50 L each (20.5 L/m2day); 4 pulses with 75 L each (41 L/m2day) and 6 pulses with 75 L each (61.6 L/m2day). In addition, the potential bioenergy generated was monitored. For the last operation condition, C1 efficiently reduced BOD5 (88.7%) and turbidity (84.4%). On the other hand, for the nutrients the treatment efficiencies were lower, with 40.3% (TP) and 46.6% (N−NH3). Overall, similar results were obtained with the C2, with mean removal efficiencies of BOD5 (87.3%), turbidity (93.1%), and lower TP (10.4%) reduction. The treatment performance presented similar tendencies even with the changes in loading rates and in hydraulic retention times. Regarding the voltage monitoring, a peak of 687 mV was obtained considering a mean loading rate of 15.6 gCOD/m2day, whereas the maximum power density was 0.25 mW/m. Future research should focus on reducing the internal resistance of the CW system, thus increasing the bioelectricity generated and in treating wastewater with higher organic matter content.

Thickness of hydrogel for nitrifying biomass entrapment determines the free ammonia susceptibility differently in batch and continuous modes

Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O2/L mL-PVA min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and -1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78–0.95 kg-N/m3 day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m3 day, while that of HG-1.13 was 0.0516 kg-FA/m3 day. In the batch mode, where wastewater is introduced all at once, the high accumulation of FA posed a disadvantage for the FA-susceptible HG-0.55, which made it unsuitable for application. However, in the continuous mode, the thinner HG-0.55, with its larger surface area and high ammonia oxidation activity, proved to be suitable and demonstrated its effectiveness. This study provides valuable insights and a framework for the utilization strategy of immobilized gels in addressing the toxic effects of FA in practical processes.

Pilot-scale study on an advanced Fe-Cu process for refractory wastewater pretreatment

The extreme pH, high color, and poor biodegradability of refractory wastewater have severe impacts on its biological treatment. To address this issue, an advanced Fe-Cu process with redox reaction and spontaneous coagulation was investigated and applied for pilot-scale (wastewater flow rate of 2000 m3·day−1) pretreatment of separately discharged acidic chemicals and alkaline dyeing wastewater. The advanced Fe-Cu process had five functions: (1) increasing the pH of chemical wastewater to 5.0 and above, with an influent pH of approximately 2.0; (2) transforming refractory organics of chemical wastewater with 10.0% chemical oxygen demand (COD) and 30.8% color removal, thereby enhancing the ratio of biological oxygen demand after five days (BOD5) to COD (B/C) from 0.21 to 0.38; (3) neutralizing the pH of the pretreated chemical wastewater for coagulation application with alkaline dyeing wastewater to avoid adding alkaline chemical; (4) achieving average nascent Fe(II) concentrations of 925.6 mg∙L−1 using Fe-Cu internal electrolysis for mixed wastewater coagulation, resulting in an average of 70.3% color removal and 49.5% COD removal; (5) providing more efficient COD removal and B/C enhancement than FeSO4∙7 H2O coagulation while avoiding secondary pollution. The green process offers an effective, easy-implemented solution for the pretreatment of separately discharged acidic and alkaline refractory wastewater.