A predictive model for determining the nitrite concentration in the effluent of an anammox reactor using ensemble regression tree algorithm.

Anaerobic ammonium oxidation (anammox) is a cost-effective biological nitrogen removal method for treating wastewater. Nitrite has strong negative effect on microbial activity of anammox bacteria, while the conventional equitment available for determining nitrite on-line is challenging due to high price. By knowing the concentration of nitrite in the effluent, its concentration in the reactor can be controlled accordingly. To investigate this, an ensemble regression tree algorithm was used to establish the predictive model proposed in the current work. Moreover, the Bayesian algorithm was adopted to systematically optimize various parameters of machine learning algorithms. The predicted concentrations of nitrite were in good agreement with the observed values, and the coefficient of determination (R2) and root mean squared error (RMSE) values reached 0.91 and 4.81, respectively. Furthermore, the model established by the ensemble regression tree algorithm was compared with models established by commonly used machine learning algorithms. Finally, the established models were applied to another anammox reactor, and the predicted results of ensemble regression tree model were found to be in good agreement with the experimental values with R2 and RMSE values of 0.84 and 6.34, respectively.

Achieving advanced nitrogen removal in a novel partial denitrification/anammox-nitrifying (PDA-N) biofilter process treating low C/N ratio municipal wastewater.

For achieving mainstream anammox, a novel partial denitrification/anammox-nitrifying (PDA-N) biofilter process to treat municipal wastewater was developed. This process achieved a total inorganic nitrogen (TIN) removal efficiency of 81%, with an average effluent TIN of 7.31 mg·L-1, when the ratio of influent chemical oxygen demand (COD) to TIN was 3.2. Approximately 97% of the TIN was removed by anammox in the PDA biofilter. Nitrite was provided by partial denitrification for anammox. Partial denitrification was driven by Thaurea in the middle and lower regions of the PDA biofilter, while anammox was mainly driven by Candidatus Brocadia in the middle and upper regions. When treating real municipal wastewater, the TIN was efficiently removed in the PDA-N biofilter, with the effluent TIN of 5.96 mg·L-1. Anammox played a primary role, achieving approximately 98% of the TIN removal. Compared to the traditional nitrification/denitrification process, this process can economize organic carbon demand and oxygen consumption.

Some issues limiting photo(cata)lysis application in water pollutant control: A critical review from chemistry perspectives.

For decades, photolysis and photocatalysis have been touted as promising environment-benign and robust technologies to degrade refractory pollutants from water. However, extensive, large-scale engineering applications remain limited now. To facilitate the technology transfer process, earlier reviews have advocated to developing more cost-effective and innocuous materials, maximizing efficiency of photon usage, and optimizing photoreactor systems, mostly from material and reactor improvement perspectives. However, there are also some fundamental yet critical chemistry issues in photo(cata)lysis processes demanding more in-depth understanding and more careful consideration. Hence, this review summarizes some of these challenges. Of them, the first and paramount issue is the interference of coexisting compounds, including dissolved organic matter, anions, cations, and spiked additives. Secondly, considerable concerns are pointed to the formation of undesirable reaction by-products, such as halogenated, nitrogenous, and sulfur-containing compounds, which might increase instead of reduce toxicity of water if inadequate fluence and catalyst/additive are supplied due to time and cost constraints. Lastly, a critical issue lies in the uncertainty of current approaches used for identifying and quantifying radicals, especially when multiple radicals coexist together under changing and interconvertible conditions. The review hence highlights the needs to better understand these fundamental chemistry issues and meanwhile calls for more delicate design of experiments in future studies to overcome these barriers.

Photolysis and photocatalysis of haloacetic acids in water: A review of kinetics, influencing factors, products, pathways, and mechanisms.

Haloacetic acids (HAAs) are a group of pollutants ubiquitous in natural environment and anthropogenic systems, and therefore in need of control. Photolysis and photocatalysis techniques via ultraviolet (UV)-based technologies have held promise for decades in degrading organic molecules in water, but their capacities in removing HAAs remain to be explored. To better understand the trends in the existing literature and to identify the knowledge gaps that may merit further exploration, this review compares the HAAs photodegradation kinetics, influencing factors, reaction products, pathways, and mechanisms for a variety of UV technologies. The selected UV processes are classified into three types: UV-only photolysis, photooxidation, and photoreduction. Overall, although trends vary significantly depending upon many factors, the photo-susceptibility of HAAs always increases with rising molecular weight of substituted halogen atom(s), with those chlorinated HAAs being the most refractory species. Notably, while many processes proved hydroxyl radical (OH) as the forcing driver, the patterns of kinetics among HAAs were not consistent among processes, suggesting that OH was not the only driver. Compared to earlier studies focusing on specific technologies to treat numerous contaminants through a material perspective, this review commits to understanding the commonalities and differences among multiple UV-based technologies in treating only one group of compound mainly via a chemistry viewpoint.

Removal of urea from swimming pool water by UV/VUV: The roles of additives, mechanisms, influencing factors, and reaction products.

To discover an applicable technology for urea abatement from swimming pool water (SPW), this study compared the performances of seven ultraviolet (UV)-based technologies on urea removal, including UV alone, UV coupled with hydrogen peroxide (UV/H2O2), sulfite (UV/Na2SO3), potassium persulfate (UV/K2S2O8), a combination of UV and vacuum UV (UV/VUV), and UV/VUV in tandem with either H2O2 (VUV/H2O2) or potassium persulfate (VUV/K2S2O8). Among them, UV and UV/Na2SO3 showed little removal ability, and UV/H2O2 removed only 12.8% of urea within 3-h experiments, while UV/VUV degraded 71.7% of urea without introducing substantial total dissolved solids (TDS). Therefore, UV/VUV was considered as a promising technology for further exploration. In comparison, although UV/K2S2O8 exhibited higher urea removal than UV/VUV, it caused dramatic increases of TDS, which made the regulatory threshold for the TDS increment difficult to maintain. Within UV/VUV studies, some common components in SPW (e.g., cyanuric acid, humic acid, nitrate, and bicarbonate) inhibited the removal process, whereas chloride and sulfate facilitated it, while free chlorine at doses ≤ 3 mg-Cl2/L and pH levels from 6.8 to 8.0 imposed little impact on urea degradation. Overall, UV/VUV degraded 40.0% and 22.2% of urea from tap water and SPW, respectively; both were lower than the efficiency observed in ultrapure water. As for reaction byproducts, urea phototransformation via UV/VUV yielded nitrate and ammonia as the key products with the mass balance of nitrogen element being met. However, the contents of organic carbon decreased at a rate slightly lower than urea degradation, suggesting that urea was mostly mineralized and slightly converted to unknown organic compounds. The results hence demonstrate that UV/VUV is an effective alternative for urea removal from SPW.

A one-year long survey of temporal disinfection byproducts variations in a consumer's tap and their removals by a point-of-use facility.

In order to better understand the occurrence of disinfection byproducts (DBPs) in tap water and their real impacts on consumers, this study made a one-year long survey of the temporal variations of a series of DBPs before and after a point-of-use (POU) treatment facility installed in a building serving for ∼300 people. Water samples were collected every week at a fixed location and time for 1 year, and frequent samplings were carried out every 6 h a day for 1 month at selected seasons, which ultimately amounted to 322 samples. The results show that the concentrations of DBPs were higher in the summer than other seasons, with the lowest DBP levels being observed in spring. Within one week, higher levels of haloacetic acids (HAAs) were identified on weekdays than those on weekends. Diurnally, trihalomethanes, HAAs, and haloacetaldehydes were found to be higher at noon but lower in the evening. Consistent with other studies, the variations of most DBPs were somewhat positively related to the changes of temperature and organic matter, but negatively related to the quantity of free chlorine. With the use of a POU facility, which equips with two activated carbon cartridges and a boiler in sequence, most of DBPs were dramatically reduced, leading to 62-100% lower cytotoxicity for the measured DBPs. The study hence provides a real-water evidence about the DBP occurrences in a typical distribution system endpoint and the efficiency of a typical POU on mitigating DBP risks.

A facile and green pretreatment method for nonionic total organic halogen (NTOX) analysis in water - Step II. Using photolysis to convert NTOX completely into halides.

Adsorbable organic halogen (AOX) is a parameter conventionally used to indicate the sum of organic halogenated disinfection byproducts (DBPs), which are formed from the reactions of disinfectants with dissolved organic matter, bromide and iodide in water. To overcome the issues of the AOX analytical method, we proposed a new facile and green pretreatment method to enable the analysis of nonionic total organic halogen (NTOX) via the following three steps: 1) separation of NTOX and halides with electrodialysis, 2) conversion of NTOX with ultraviolet (UV) photolysis, and 3) analysis of halides with ion chromatography. To verify this proposal, we mainly evaluated the efficiency of vacuum ultraviolet (VUV) coupled with UV photolysis (VUV-UV) in converting NTOX into halides. Results showed that by applying VUV irradiation for 60 min and UV irradiation at pH 10-11 for another 30 min, over 85.5% of each halide from 20 representative small molecular weight DBPs (each at 100 µg-X/L level) was recovered. The purpose of UV photolysis under alkaline conditions was to reduce oxyhalides (such as bromate and iodate) formed in the VUV process back to halides. With the aid of electrospray ionization-triple quadrupole mass spectrometry, we captured the whole pictures of high molecular weight polar DBPs in a chlorinated drinking water before and after VUV-UV, through which averagely 96.4% of dehalogenation with the VUV-UV treatment was observed. An illustrative comparison of the conventional AOX method and the proposed NTOX method indicates that although the detected NTOX was lower (by 2.3-30.6%) than AOX, the results of the two methods were highly correlated (R2 > 0.97). All these hence verified the photolysis as a mature yet novel tool for sample pretreatment in environmental analytical chemistry.

A facile and green pretreatment method for nonionic total organic halogen (NTOX) analysis in water - Step I. Using electrodialysis to separate NTOX and halides.

Adsorbable organic halogen (AOX) is a bulk organic parameter conventionally used to indicate all adsorbable halogenated organic disinfection byproducts formed in disinfected water. Analytically, AOX is determined by three sequential steps: 1) concentration and separation of AOX from halides with activated carbon, 2) conversion of AOX into halides with pyrolysis, and 3) quantification of halides via microcoulometry or ion chromatography (IC). Because the approach is relatively costly and cannot effectively recover non-adsorbable compounds, we herein proposed a facile and green pretreatment tool to measure the nonionic portion of total organic halogen (NTOX) with a new three-step approach: 1) separation of NTOX and halides with electrodialysis (ED), 2) conversion of NTOX into halides with ultraviolet, and 3) analysis of halides with IC. To verify this proposal, this study presented the efficiency of ED in separating halides and NTOX under a variety of operational and environmental conditions. The results showed that ED removed ≥98.5% of fluoride, chloride, bromide, and iodide from all tested waters (up to 1000 mg-X/L) within 1.5 h. Meanwhile, ED recovered an average of 87.9% of fourteen small molecular weight model compounds with each at 100 µg/L. By using electrospray ionization-triple quadrupole mass spectrometry, the whole pictures of high molecular weight compounds in a chlorinated drinking water before and after ED pretreatment were compared, which revealed 79.7% and 83.6% recoveries of overall polar chlorinated and brominated compounds, respectively. In addition, the quantity and property of the dissolved organic matter were largely maintained by ED, and the retained organics may be used for later characterization. The study hence presents a novel use of ED as a pretreatment tool to enable subsequent NTOX measurement.