Huiyu Dong

Effect of artificial aeration on the performance of vertical-flow constructed wetland treating heavily polluted river water

Three lab-scale vertical-flow constructed wetlands (VFCWs), including the non-aerated (NA), intermittently aerated (IA) and continuously aerated (CA) ones, were operated at different hydraulic loading rates (HLRs) to evaluate the effect of artificial aeration on the treatment efficiency of heavily polluted river water. Results indicated that artificial aeration increased the dissolved oxygen (DO) concentrations in IA and CA, which significantly favored the removal of organic matter and NH(4+)-N. The DO grads caused by intermittent aeration formed aerobic and anoxic regions in IA and thus promoted the removal of total nitrogen (TN). Although the removal efficiencies of COD(Cr), NH(4+)-N and TN in the three VFCWs all decreased with an increase in HLR, artificial aeration enhanced the reactor resistance to the fluctuation of pollutant loadings. The maximal removal efficiencies of COD(Cr), NH(4+)-N and total phosphorus (TP) (i.e., 81%, 87% and 37%, respectively) were observed in CA at 19 cm/day HLR, while the maximal TN removal (i.e., 57%) was achieved in IA. Although the improvement of artificial aeration on TP removal was limited, this study has demonstrated the feasibility of applying artificial aeration to VFCWs treating polluted river water, particularly at a high HLR.

A comparison of various rural wastewater treatment processes for the removal of endocrine-disrupting chemicals (EDCs)

The removal of six endocrine-disrupting chemicals (EDCs), including estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinyl estradiol (EE2), bisphenol A (BPA) and 4-nonylphenol (NP), was investigated in 20 rural wastewater treatment facilities (WWTFs) located in a county of Zhejiang Province, China. These WWTFs adopted one of the four treatment processes: activated sludge (AS), constructed wetland (CW), stabilization pond (SP), and micro-power biofilm reactor (MP). Results indicate that all the six EDCs were detected in wastewater samples with NP showing a maximum detection frequency (97%) and a maximum influent concentration (5002 ng L(-1)). After biological treatment, the concentrations of E2, E3 and NP decreased remarkably, while E1, EE2 and BPA exhibited varying removal efficiencies that depended on the specific treatment process and sampling season. In general, the centralized AS process outperformed those decentralized processes (i.e., CW, SP and MP) and a higher removal of E1, EE2, NP and BPA in the AS process was observed in summer (>70%) than in winter. Among the three decentralized processes, the removal of EDCs in the SP process was limited, especially for E1, EE2 and BPA (18-46%) in winter. Due to an incomplete removal, the total concentration of target EDCs increased obviously in the mixing and downstream sections of a local river receiving the effluent from a typical WWTF (practicing AS). This study reveals that the design and operation of rural WWTFs should be optimized if an effective removal of EDCs is to be achieved.

Evaluation of rural wastewater treatment processes in a county of eastern China.

With the rapid urbanization and industrialization in China, wastewater treatment in rural areas has become an increasing national concern. The selection of appropriate treatment processes closely based on the actual local status is crucial for the prevention of water quality deterioration in rural areas of China. This study presents a full year survey on the performances of various rural wastewater treatment processes at a county level in eastern China including seven three-chamber septic tanks (ST), five micro-power biological facilities (MP), seven constructed wetlands (CW), three stabilization ponds (SP) and five centralized activated sludge treatment plants (AS). It was found that although ST could remove a notable portion of total suspended solids (TSS) and chemical oxygen demand (COD(Cr)), it was ineffective in reducing nutrients and pathogens. Reliability and stability analyses showed that the centralized AS and decentralized CW processes outperformed the SP and MP processes. There were obvious discrepancies between the mean design concentrations, which ensure that 95% of the effluents meet the discharge standards, and the actual effluent concentrations determined for each process. The expected compliance with the tentatively adopted second-grade discharge standards (GB 18918-2002) was unsatisfactory for most of the water quality parameters examined, indicating an urgent need to design more practical discharge standards for decentralized treatment processes. Based on an overall assessment of reliability, stability and cost-effectiveness, the centralized AS was suitable for densely populated towns while the decentralized CW was suitable for sparsely populated villages.

Formation of iodo-trihalomethanes, iodo-acetic acids, and iodo-acetamides during chloramination of iodide-containing waters: Factors influencing formation and reaction pathways.

This study investigated systematically the factors influencing the formation of iodinated disinfection by-products (I-DBPs) during chloramination of I--containing waters, including reaction time, NH2Cl dose, I- concentration, pH, natural organic matter (NOM) concentration, Br-/I- molar ratio, and water matrix. Among the I-DBPs detected, iodoform (CHI3), iodoacetic acid (IAA), diiodoacetic acid (DIAA), triiodoacetic acid (TIAA), and diiodoacetamide (DIAcAm) were the major species produced from reactions between reactive iodine species (HOI/I2) and NOM. A kinetic model involving the reactions of NH2Cl auto-decomposition, iodine species transformation and NOM consumption was developed, which could well describe NH2Cl decay and HOI/I2 evolution. Higher concentrations of CHI3, IAA, DIAA, TIAA, and DIAcAm were observed in chloramination than in chlorination, whereas IO3- was only formed significantly in chlorination. Maximum formation of I-DBPs occurred at pH 8.0, but acidic conditions favored the formation of iodinated haloacetic acids and DIAcAm. Increasing Br-/I- molar ratio from 1 to 10 did not increase the total amount of I-DBPs, but produced more bromine-substituting species. In addition, chloramination of 18 model compounds indicated that low-SUVA254 (specific ultraviolet absorbance at 254nm) NOM generally favored the formation of I-DBPs compared to high-SUVA254 NOM. Finally, potential pathways for I-DBPs formation from chloramination of NOM were proposed.

Formation and speciation of disinfection byproducts during chlor(am)ination of aquarium seawater

The chemistry associated with the disinfection of aquarium seawater is more complicated than that of freshwater, therefore limited information is available on the formation and speciation of disinfection byproducts (DBPs) in marine aquaria. In this study, the effects of organic precursors, bromide (Br-) and pre-ozonation on the formation and speciation of several typical classes of DBPs, including trihalomethanes (THM4), haloacetic acids (HAAs), iodinated trihalomethanes (I-THMs), and haloacetamides (HAcAms), were investigated during the chlorination/chloramination of aquarium seawater. Results indicate that with an increase in dissolved organic carbon concentration from 4.5 to 9.4 mg/L, the concentrations of THM4 and HAAs increased by 3.2-7.8 times under chlorination and by 1.1-2.3 times under chloramination. An increase in Br- concentration from 3 to 68 mg/L generally enhanced the formation of THM4, I-THMs and HAcAms and increased the bromine substitution factors of all studied DBPs as well, whereas it impacted insignificantly on the yield of HAAs. Pre-ozonation with 1 mg/L O3 dose substantially reduced the formation of all studied DBPs in the subsequent chlorination and I-THMs in the subsequent chloramination. Because chloramination produces much lower amounts of DBPs than chlorination, it tends to be more suitable for disinfection of aquarium seawater.

Enhanced formation of bromate and brominated disinfection byproducts during chlorination of bromide-containing waters under catalysis of copper corrosion products

Copper corrosion products (CCPs) in water distribution pipes may catalyze the reactions among disinfectant, natural organic matter (NOM), and bromide (Br(-)). This study investigated the simultaneous formation of bromate (BrO3(-)) and brominated disinfection byproducts (Br-DBPs) during chlorination of Br(-)-containing waters in the presence of three CCPs (i.e., CuO, Cu2O, and Cu(2+)). In a synthetic water, both oxidant decay and BrO3(-) formation were enhanced by CCPs, whereas the presence of humic acid (HA) significantly inhibited BrO3(-) formation due to its competition for HOBr to form Br-DBPs. In the HOClBr(-)CuO system, the BrO3(-) yield increased obviously with increasing CuO dose and initial Br(-) concentration, while the catalytic formation of Br-DBPs was rather limited. A molar conversion (Br(-) to BrO3(-)) of 22.1% was observed under CuO catalysis, compared with little conversion in the absence of CuO. In the HOClBr(-)Cu2O/Cu(2+) systems, Cu2O or Cu(2+) mainly enhanced the formation of Br-DBPs, with enhancement ratios of 69.9% and 50.1%, respectively. The degree of enhancement on Br-DBPs formation became more apparent with increasing pH, while that on BrO3(-) formation reached maximal at pH 7.6. The catalytic formation of Br-DBPs and BrO3(-) by CCPs was also verified in three filtered real waters, although to a lesser extent because of the water matrix effect. In mechanism, the CCPs promoted the formation of BrO3(-) and Br-DBPs through catalyzing the HOBr disproportionation pathway and the reaction of HOBr toward HA, respectively.

Monitoring free chlorine and free bromine in aquarium seawater treated by ozone

Free chlorine (FC) and free bromine (FB) produced during ozonation treatment of aquarium seawater pose a serious threat to the health of ornamental aquatic animals, but little is known about the concentration levels of these chemicals in aquarium facilities. In this study, a highly selective and sensitive analytical method based on the derivatization of FC and FB to corresponding 4-halo-2,6-dimethylphenols by 2,6-dimethylphenol was developed. The formed halo-derivatives were extracted by hexane and subsequently quantified by gas chromatography-mass spectrometry. The calibration curves showed good linearity (r2 > 0.999) in a broad concentration range of 2.1–4200 μg L−1 for FC and 3.3–1700 μg L−1 for FB. The method detection limits (S/N = 3) were determined to be 62.7 and 71.6 ng L−1 for FC and FB, respectively. The developed method exhibited good recovery, selectivity, precision and was successfully applied to monitor the formation and decay of FC and FB in ozonated seawater. During the ozonation process, the formation of FB dominated, while much less chloride was oxidized to FC; FB decayed much faster than FC. The concentrations of FC and FB in various animal tanks of Beijing Aquarium were also monitored. The results show that 30.1–56.4 μg L−1 FC and 26.5–730.7 μg L−1 FB were present in aquarium tanks, revealing that the health of aquatic animals (particularly fish, jellyfish, and coral) was under severe threat.

Adsorption of phenolic compounds from water by a novel ethylenediamine rosin-based resin: Interaction models and adsorption mechanisms

This study describes the adsorption performance of a novel ethylenediamine rosin-based resin (EDAR) for several industrially-important phenolic compounds. Its removal of 4-nitrophenol (4-NP) from water was comparable to or better than many commercial resins, although it was less effective with other phenols (i. e., phenol, 2,4-dichlorophenol, 4-chlorophenol, and 4-methylphenol). Experimental conditions for batch adsorption of 4-NP by EDAR are evaluated, the adsorption kinetics is well described by the pseudo-second-order model (R2 > 0.99) and isotherm follows the Langmuir isotherm model (R2 > 0.99), with the maximum monolayer adsorption capacity of 82 mg g-1 at pH 6.0 and 293 K. The thermodynamic parameters indicate that the adsorption is spontaneous and endothermic. Also, quantum chemistry calculations indicate involvement of hydrogen-bonding between 4-NP and amino groups of EDAR. 4-NP was efficiently desorbed from the loaded EDAR resin by 0.2 M HCl, and the resin could be recycled with only a small decrease in its initial adsorption capacities. Thus, EDAR is a promising adsorbent for the removal of 4-NP during water treatment.

Quinone group enhances the degradation of levofloxacin by aqueous permanganate: Kinetics and mechanism

Quinone group is an important fraction of humic acid. The pseudo-first-order rate constant (kobs) of levofloxacin (LF) degradation by permanganate (MnO4-) significantly increased from 0.010 (without benzoquinone, BQ) to 0.042-0.443 min-1 at [BQ]o:[MnO4-]o (molar ratio) = 0.03-0.25 at pH 7.5, and an acidic pH facilitated LF degradation. In the presence of BQ, MnO4- was first reduced to Mn(II). Then, Mn(II) reacted with BQ to produce Mn(III) and semiquinone radical, which was promoted under acidic conditions. With dissolved oxygen available, Mn(III) further oxidized semiquinone radical to produce singlet oxygen (1O2) and superoxide radical (O2-) as well as regenerate BQ. In addition, MnO4- could also react with Mn(II) to produce Mn(III), whose complexation with semiquinone radical in turn promoted this reaction. Due to the predominant scavenging of O2- by BQ, 1O2 and Mn(III) mainly contributed to the accelerated LF degradation, with a notable formation of hydroxyl, ketone and endoperoxide groups in the degradation byproducts. This study helps better understand the role of natural organic matter in the degradation of organic micropollutants by MnO4- in water treatment.

Is anammox a promising treatment process for nitrogen removal from nitrogen-rich saline wastewater?

Rapidly growing discharge of nitrogen-rich saline wastewater has significantly affect environment. However, due to the inhibition resulting from high salinity on microbes, it is still a challenge to treat nitrogen-rich saline wastewater efficiently. Anammox process, as a cost-effective and environment-friendly nitrogen removal approach, has shown a potential in treating nitrogen-rich saline wastewater. This review is conducted from a critical perspective and provides a comprehensive overview on the performance of anammox process treating nitrogen-rich saline wastewater. Two strategies including freshwater-derived anammox bacteria acclimatization and marine anammox bacteria enrichment are evaluated. Second, effects resulting from salinity on the performance of anammox reactor, the microbial communities and sludge characteristics are discussed. Third, salinity-tolerant mechanism of anammox bacteria is analyzed. This review also reveals some critical knowledge gaps and future research needs, which benefits application of anammox process to treat nitrogen-rich saline wastewater.