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The industrial laundry sector is a major user of water and chemicals such as surfactants, and one of the largest producers of wastewater. Although treated wastewaters comply with regulations, they still contain contaminants. Here we review laundry wastewater with focus on industrial laundry activities and their challenges, chemical composition of wastewater, and treatment techniques. We discuss advantages and drawbacks of treatment techniques that can be used as secondary treatment in already existing plants, or as tertiary treatment, i.e., complementary to an existing treatment. We observe that laundry is an expanding industrial sector with increasing water requirements, an abundant use of chemical substances, and increasingly stringent discharge regulations. There is a lack of chemical and biological knowledge on aqueous discharges. Moreover, the chemical composition, temporal variability, treatment information, and environmental and ecotoxicological data are poorly reported. The composition of wastewaters and additives, and their temporal variability are also poorly known. Similarly, detailed information on treatments is rare, and environmental and ecotoxicological data are poorly reported. Finding a tertiary water treatment process that is efficient, viable, and environmentally friendly is challenging since wastewater volumes are very high and contaminants are present at trace level in complex organo-mineral mixtures.

The challenge of water reclamation using membranes in this study was the quite unique wastewater composition resulting from a high share of biotech wastewater. The high content of organic matter and high concentrations of calcium, bicarbonate, and sulphate were considered as challenging for membrane processes. Consequently, an innovative ultra-tight ultrafiltration (u-t UF) membrane was developed and tested on-site at pilot scale. In comparison, a conventional UF and an open nanofiltration (NF) were piloted. The aim was to find the best pre-treatment option for reverse osmosis (RO) to reduce fouling and scaling and produce fit-for-purpose water; for example, cooling. Overall, the quality of the currently used water source was surpassed by the pilot plant. Only a standard post-treatment of the RO permeate was necessary for stabilisation. Results indicated that denser membranes only minimally reduced fouling of RO. An assessment comparing the treatment trains in a life cycle assessment using the data collected from the pilot operation (UF/NF operating settings, RO plant performance, and the design of multi-stage industrial scale RO) revealed lower greenhouse gas emissions compared to seawater desalination. However, if the RO brine treatment becomes mandatory, the greenhouse gas emissions from water reclamation and supply will be higher than those from freshwater supply.

This study aimed to investigate the spatial distribution of micropollutants in wastewater related to catchment area, and their environmental risks and fate. About 24-h flow proportional effluent ( n  = 26) wastewater samples were collected from eight WWTPs across Denmark. From five of these WWTPs corresponding influent samples ( n  = 20) were collected. Samples were enriched by multi-layer solid phase and analysed by liquid chromatography–high-resolution mass spectrometry and comprehensive two-dimensional gas chromatography with high-resolution mass spectrometry detection. We detected and quantified 79 micropollutants from a list of 291 micropollutants in at least one influent or effluent wastewater sample. From this we found that 54 micropollutants decreased in concentrations during wastewater treatment, while O-desmethylvenlafaxine, carbamazepine, amitriptyline, benzothiazole, terbutryn, and citalopram increased in concentrations through the WWTP. The toxicity of effluent wastewater samples was assessed by EC50 using Raphidocelis subcapitata ( R. subcapitata ) and LC50 using the crustacean Daphnia magna ( D. Magna ), for which six micropollutants were detected above the predicted no-effect concentration. Our study demonstrates that catchment area influences the micropollutant composition of wastewater. Out of 19 pharmaceuticals, the measured concentration in influent wastewater was predicted within a factor of 10 from sale numbers and human excretion, which demonstrates the strong influence of catchment area on micropollutant composition.

Lemnaceae, i.e. duckweed species, are attractive for phytoremediation of wastewaters, primarily due to their rapid growth, high nutrient uptake rates, tolerance to a broad range of growing conditions and ability to expeditiously assimilate a variety of pollutants. Light is essential for plant growth, and therefore, phytoremediation. Nevertheless, the effect of light intensity remains poorly understood in relation to phytoremediation, a knowledge gap that impedes the development of indoor, fully controlled, stacked remediation systems. In the present study, the effect of light intensity (10–850 μmol m −2  s −1 ) on the phytoremediation potential of Lemna minor was assessed. Plants were grown on either an optimal growth medium (half-strength Hutner’s) or synthetic dairy processing wastewater, using stationary axenic (100 mL) or re-circulating non-sterile (11.7 L) systems. The relative growth rate (RGR) of L. minor grown on half-strength Hutner’s increased proportionally with increasing light intensity. In contrast, the RGR of L. minor grown on synthetic dairy wastewater did not increase with light over an intensity range from 50 to 850 μmol m −2  s −1 . On synthetic dairy wastewater, total nitrogen and total phosphorous removal also remained unchanged between 50 and 850 μmol m −2  s −1 , although L. minor protein content (% fresh weight) increased from 1.5 to 2% at higher light intensities. Similar results were obtained with the larger re-circulating system. The results demonstrate interactive effects of light intensity and wastewater composition on growth and phytoremediation potential of L. minor . The data imply that light intensities above 50 μmol m −2  s −1 may not necessarily confer benefits in duckweed wastewater remediation, and this informs engineering of stacked, indoor remediation systems.

In a wastewater treatment plant (WWTP), several sludge streams exist and the composition of their liquid phase varies with time and place. For evaluating the potential for formation of precipitates and equilibria for weak acids/bases, the ionic strength and chemical composition need to be known. This information is often not available in literature, and even neglected in chemical model-based research. Based on a literature review, we proposed three ranges of concentration (low, typical and high) for the major constituents of the liquid phase of the different streams in a WWTP. The study also discusses the reasons for the concentration evolution, and the exceptional cases, to allow readers to consider the right range depending on their situation. The ionic strength of the different streams and the contribution of its constituents were calculated based on the ionic composition. The major contributors to the ionic strength for the wastewater-based streams (influent, effluent and mixed sludge) were Na+, Cl−, Mg2+ and Ca2+, representing 50–70% of the ionic strength. For digestate, and accounted for 65–75% of the ionic strength. Even though the ionic strength is recognized to impact several important wastewater treatment processes, its utilization in literature is not always adequate, which is discussed in this study.

Microalgae represent an alternative to conventional wastewater treatment, potentially improving antibiotic removal and offering a solution to combat the spread of antimicrobial resistance. Through batch assays, this study investigates the routes for antibiotic removal using three strains (Chlamydomonas acidophila, Auxhenochlorella protothecoides and Tetradesmus obliquus). Using mixtures of ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole, and trimethoprim at concentrations simulating wastewater composition, it also assesses antibiotic effects on microalgae physiology. The three strains primarily removed antibiotics through rapid biosorption, achieving up to 91.5% removal for specific ones like ciprofloxacin. T. obliquus and C. acidophila showed efficacy, with total removals of 37.2% and 49.3%, respectively. Over time, A. protothecoides demonstrated the highest active removal efficiency, eliminating 22.1% of total antibiotics, with a notable 67.6% removal for sulfamethoxazole. Abiotic degradation through hydrolysis and photolysis contributed to ciprofloxacin, ofloxacin, clarithromycin, and erythromycin removal (34.7% to 96.7%), showing pH-dependent photolysis. However, algae induced a shading effect, reducing the photolytic and hydrolytic degradation of specific antibiotics. T. obliquus and C. acidophila were inhibited by antibiotics, whereas A. protothecoides showed a 30.6% growth rate increase. The stimulatory effect was also observed for the nutrient removal, with A. protothecoides showing a 46.6% increase in ammonium removal and a 44.8% increase in phosphate removal with antibiotics. Additionally, antioxidant activities remained stable, except for a notable increase in peroxidase activity for A. protothecoides and T. obliquus. The study confirms efficient antibiotic removal and stimulatory responses in the three algal strains, indicating their potential for wastewater treatment and combating antimicrobial resistance.

The imminent arrival of nanoparticles (NPs) to the wastewater treatment plants (WWTP) brings concern about their effects, which can be related to the wastewater composition. In this work, the effects of titanium dioxide (TiO 2 ) NPs in the removal of carbon, nitrogen, and phosphorus by activated sludge bioreactors during the treatment of synthetic, raw, and filtered wastewaters were evaluated. Floc size, compaction of sludge, and morphological interactions between sludge and NPs were also determined. The main effect of TiO 2 NPs was the inhibition of up to 22% in the removal of ammonia nitrogen for all types of wastewaters. This effect is strong dependent on combined factors of TiO 2 NPs concentration and content of organic matter and ammonia in wastewater. The removal of dissolved organic carbon was affected by TiO 2 NPs in lower level (up to 6%) than nitrogen removal for all types of wastewaters. Conversely to adverse effects, the removals of orthophosphate in the presence of TiO 2 NPs were improved by 34%, 16%, and 55% for synthetic, raw, and filtered wastewater, respectively. Compaction of the sludge was also enhanced as the concentrations of NPs increased without alterations in the floc size for all types of wastewaters. Based on TEM and STEM imaging, the main interaction between TiO 2 NPs and the activated sludge flocs was the adsorption of NPs on cell membrane. This means that NPs can be attached to cell membrane during aerobic wastewater treatment, and potentially disrupt this membrane. The effects of TiO 2 NPs on macronutrient removal clearly depended on wastewater characteristics; hence, the use of realistic media is highly encouraged for ecotoxicological experiments involving NPs.

A new set up of the integral mechanistic BIO_ALGAE model that describes the complex interactions in mixed algal-bacterial systems was developed to overcome some restrictions of the model. BIO_ALGAE 2 includes new sub-models that take into account the variation of microalgae and bacteria performance as a function of culture conditions prevailing in microalgae cultures (pH, temperature, dissolved oxygen) over daily and seasonal cycles and the implementation of on-demand dioxide carbon injection for pH control. Moreover, another aim of this work was to study a correlation between the mass transfer coefficient and the hydrodynamics of reactor. The model was calibrated using real data from a laboratory reactor fed with real wastewater. Moreover, the model was used to simulate daily variations of different components in the pond (dissolved oxygen, pH, and CO 2 injection) and to predict microalgae ( X ALG ) and bacteria ( X H ) proportions and to estimate daily biomass production ( C b ). The effect of CO 2 injection and the influence of wastewater composition on treatment performance were investigated through practical study cases. X ALG decreased by 38%, and X H increased by 35% with respect to the system under pH control while microalgae and bacteria proportions are completely different as a function of influent wastewater composition. Model simulations have indicated that C b production (~ 100 gTSS m −3  day −1 for manure and centrate) resulted lower than C b production obtained using primary influent wastewater (155 gTSS m −3  day −1 ).

Using microalgae to treat wastewater has received growing attention in the world because it is regarded as a novel means for wastewater treatment. It is commonly recognized that large-scale cultivation and commercial application of microalgae are limited by the development of photobioreactor (PBR). Although there are a lot of PBRs for microalgae pure cultivation which used culture medium, specialized PBRs designed for wastewater treatment are rare. The composition of wastewater is quite complicated; this might cause a very different photosynthetic effect of microalgae compared to those grown in a pure cultivation medium. Therefore, PBRs for wastewater treatment need to be redesigned and improved based on the existing PBRs that are used for microalgae pure cultivation. In this review, different PBRs for microalgae cultivation and wastewater treatment are summarized. PBR configurations, PBR design parameters and types of wastewater are presented. In addition, the wastewater treatment efficiency and biomass productivity were also compared among each type of PBRs. Moreover, some other promising PBRs are introduced in this review, and a two-stage cultivation mode which combines both closed and open system is discussed as well. Ultimately, this article focuses on current problems and gives an outlook for this field, aiming at providing a primary reference for microalgae cultivation by using wastewater.

The Kingdom of Saudi Arabia is facing an acute shortage of high-quality water, which is further aggravated due to inadequate and nonrenewable groundwater resources. Hence, it is crucial to explore other alternatives, such as natural wastewater treatment (phytoremediation), for water supplies that can both lower the dependence on groundwater resources and overcome the challenges and limitations associated with conventional wastewater treatment technologies. Therefore, the main objective of this research was to study the performance and efficiency of green plants such as Typha latifolia L. ( T. latifolia ) (broadleaf cattail) and Phragmites australis (Cav.) Train, ex Steud. ( P. australis ) (common reed) for wastewater treatment in eastern Saudi Arabia. The experiment was conducted in fiberglass tanks (each with a capacity of 4.0 × 7.0 × 0.5 m 3 ) in the field. There were a total of 4 fiberglass tanks with 2 replications. A percent decrease of 72.86% and 49.74%, 39.30% and 18.07%, 39.84% and 52.87%, 38.73% and 40.86%, 74.49% and 57.82%, and 66.82% and 63.14% was observed for turbidity, TSS, nitrate, ammonia, BOD, and COD by growing P. australis and T. latifolia , respectively. Heavy metals such as aluminum, zinc, and arsenic showed a considerable reduction in pollutants in treated water compared to raw wastewater under both plants. Overall, it appears that the improvement in wastewater quality was better by growing P. australis than T. latifolia ; however, there were no statistically significant differences ( p  > 0.05) between the two plant means in their performance of raw wastewater treatment. The study results indicate that green plants could be used in a phytoremediation system to treat wastewater in rural and small communities.