Temperature and desorption mode matter in capacitive deionization process for water desalination.

Literature reporting temperature and desorption mode as factors of capacitive deionization (CDI) process for water desalination is rare. This study explored the impacts of four water temperatures (15°C, 25°C, 35°C, and 45°C), three salt concentrations (350, 1260, and 3100 mg/L), and three desorption modes (potential removal, short circuit, and polarity reversal) on performance of a 'closed-loop' CDI system. Results showed that a higher temperature promoted adsorption and desorption rates but impaired adsorption capacity. Polarity reversal could greatly expedite the desorption process compared to short circuit and potential removal. A promotional impact of concentration on CDI desalination could be explained by the formation of electrical double layers. The research also noted the earlier occurrence of re-adsorption at higher temperatures during polarity-reversal desorption. Strategies of increasing water temperature on short adsorption cycles and using an adjustable combination mode of polarity reversal and short circuit for desorption are implied for improving desalination efficiency and water recovery of CDI systems.

Variability of residual chlorine in swimming pool water and determination of chlorine consumption for maintaining hygienic safety of bathers with a simple mass balance model.

Trial-and-error chlorination as a conventional practice for swimming pool water disinfection may fail to consistently maintain the pool's residual chlorine within regulatory limits. This study explored the variability of residual chlorine and other common water quality parameters of two sample swimming pools and examined the potential of using a mass balance model for proactive determination of chlorine consumption to better secure the hygienic safety of bathers. A lightly loaded Pool 1 with a normalized bather load of 0.038 bather/m3/day and a heavily loaded Pool 2 with a normalized bather load of 0.36 bather/m3/day showed great variances in residual free and combined chlorine control by trial-and-error methods due to dynamic pool uses. A mass balance model based on chemical and physical chlorine consumption mechanisms was found to be statistically valid using field data obtained from Pool 1. The chlorine consumption per capita coefficient was determined to be 4120 mg/bather. The predictive method based on chlorine demand has a potential to be used as a complementary approach to the existing trial-and-error chlorination practices for swimming pool water disinfection. The research is useful for pool maintenance to proactively determine the required chlorine dosage for compliance of pool regulations.

Formation of disinfection by-products under influence of shale gas produced water.

Accidental spills and surface discharges of shale gas produced water could contaminate water resources and generate health concerns. The study explored the formation and speciation of disinfection by-products (DBPs) during chlorination of natural waters under the influence of shale gas produced water. Results showed the presence of produced water as low as 0.005% changed the DBP profile measurably. A shift to a more bromine substitution direction for the formation of trihalomethanes, dihaloacetic acids, trihaloacetic acids, and dihaloacetonitriles was illustrated by exploring the individual DBP species levels, bromine substitution factors, and DBP species fractions, and the effect was attributable to the introduction of bromide from produced water. The ratio of dichloroacetic and trichloroacetic acids also increased, which was likely affected by different bromination degrees at elevated bromide concentrations. Increasing blend ratios of produced water enhanced the formation of DBPs, especially the brominated species, while such negative effects could be alleviated by pre-treating the produced water with ozone/air stripping to remove bromide. The study advances understandings about the impacts of produced water spills or surface discharges regarding potential violation of Stage 2 DBP rules at drinking water treatment facilities.

A feasibility study of disinfection by-product precursor removal from surface water by a membrane bioreactor acclimatized with wastewater organic matter.

A membrane bioreactor (MBR) acclimatized with wastewater organic matter was employed for surface water treatment, and the feasibility of the MBR for the removal of disinfection by-product (DBP) precursors was studied. With a low pressure microfiltration hollow-fiber membrane module, a hydraulic retention time of 1.5 hours and a solids retention time of 180 days, the MBR was able to achieve 35% removal of trichloroacetic acid precursors and 21% removal of dichloroacetic acid precursors. The removal of trichloromethane (TCM) and brominated DBP precursors was unsatisfactory. The TCM yield and bromine substitution factors for trihalomethanes and dihaloacetic acids increased. The phenomena could be attributed to an extended treatment time for hydrophobic dissolved organic matter (DOM), production of soluble microbial products from biomass activities, and an increased Br/DOM ratio by the MBR. Since the MBR treatment would lead to the production of some new DBP precursors and a change of DOM composition, the toxic potency of the DBPs formed needs to be taken into consideration if this process is employed for surface water treatment.

Impacts of shale gas production wastewater on disinfection byproduct formation: An investigation from a non-bromide perspective.

The rapid rise of shale gas development has triggered environmental and human health concerns due to its impacts on water resources, especially on disinfection byproduct (DBP) formation upon chlorination. Despite the recently reported results on bromide, the effects of non-bromide ions in production wastewater at extremely high levels are vaguely defined. In this study, we investigated the effects of production wastewater, with bromide and non-bromide species, on the formation of DBPs when production wastewater was spiked into surface waters at various percentages. Results showed that the introduction of debrominated production wastewater led to increased formation of some chlorinated DBP species in selected surface water and wastewater. As the spiking percentage of debrominated production wastewater increased, the chlorinated DBP species increased. The contributions of individual cations to DBP formation followed a sequence of magnesium > calcium > barium at 0.10% spiking percentage due to the different catalytic effects of their chelates with organic precursors. The study of anions suggested that the discharge of treated production wastewater containing elevated sulfate may further enhance DBP formation. The significance of this study lies in the fact that in addition to bromide concerns from production wastewater, non-bromide species also contributed to DBP formation. The gas production wastewater management decision should consider the negative impacts from both bromide and non-bromide species to better protect the receiving water resources.

Novel ZnFe2O4/TiO2/flake graphite composite as particle electrodes for efficient photoelectrocatalytic degradation of rhodamine B in water.

A novel ZnFe2O4/TiO2/flake graphite composite material was synthesized and used as particle electrodes in a photoelectrocatalytic (PEC) system to investigate the degradation of rhodamine B as a model dye pollutant in water. Results showed that a PEC process with the new composite evidently led to enhanced degradation of rhodamine B due to a synergistic effect of photocatalysis and electrocatalysis. Operating variables including electrolyte concentration, applied cell voltage, air flow, composite dosage, solution pH, and dye concentration were also found to play important roles in rhodamine B removal. A 99.0% removal efficiency was observed within 30 min of treatment under optimum conditions of 0.01 mol/L Na2SO4, applied cell voltage of 15 V, air flow of 20 mL/min, composite dosage of 10 g/L, solution pH of 2, and rhodamine B concentration of 20 mg/L, with a pseudo-first-order rate constant of 0.278 min-1. These findings could provide new insights into the development of efficient PEC technologies on degradation of residual dyes in water.

Effect of capacitive deionization on disinfection by-product precursors.

Formation of brominated disinfection by-products (DBPs) from bromide and natural organic matter upon chlorination imposes health risks to drinking water users. In this study, capacitive deionization (CDI) was evaluated as a potential process for DBP precursor removal. Synthetic humic acid and bromide containing saline water was used as model water prior to CDI treatment. Batch experiments were conducted at cell voltages of 0.6-, 0.9-, and 1.2V to study the influence of CDI on the ratio of bromide and dissolved organic carbon, bromine substitution factor, and DBP formation potential (FP). Results showed beneficial aspects of CDI on reducing the levels of these parameters. A maximum DBPFP removal from 1510 to 1160µg/L was observed at the cell voltage of 0.6V. For the removed DBPFP, electro-adsorption played a greater role than physical adsorption. However, it is also noted that there could be electrochemical oxidations that led to reduction of humic content and formation of new dichloroacetic acid precursors at high cell voltages. Because of the potential of CDI on reducing health risks from the formation of less brominated DBPs upon subsequent chlorination, it can be considered as a potential technology for DBP control in drinking water treatment.

Biologically active carbon filtration for haloacetic acid removal from swimming pool water.

A biologically activate carbon (BAC) filter was continuously operated on site for the treatment of haloacetic acids (HAAs) in an outdoor swimming pool at an average empty bed contact time (EBCT) of 5.8 min. Results showed that BAC filtration was a viable technology for direct removal of HAAs from the pool water with a nominal efficiency of 57.7% by the filter while the chlorine residuals were 1.71 ± 0.90 mg/L during the study. THMs and TOC were not removed and thus were not considered as indicators of the effectiveness of BAC filtration. Increased EBCT in the range of 4.5 and 6.4 min led to improved HAA removal performance, which could be best fit by a logarithmic regression model. BAC filtration also affected the HAA speciation by removing more dichloroacetic acid (DCAA) than trichloroacetic acid (TCAA), resulting in a lower ratio of DCAA/TCAA in the filtered effluent. However, the observation of an overall constant ratio could be attributable to a complex formation and degradation mechanism occurring in swimming pools.

Metabolic Degradation of 1,4-dichloronaphthalene by Pseudomonas sp. HY.

There is increasing concern regarding the adverse health effects of polychlorinated naphthalenes (PCNs). The metabolic degradation of 1,4-dichloronaphthalene (1,4-DCN) as a model PCN, was studied using a strain of Pseudomonas sp. HY. The metabolites were analyzed by gas chromatography-mass spectrometry (GC-MS). A series of metabolites including dihydroxy-dichloro-naphthalene, epoxy-dichlorinated naphthalene, dichlorinated naphthol, and dichlorinated salicylic acid were identified. The time-concentration plots of the degradation curves of 1,4-DCN was also obtained from the experiments, which set the initial concentration of 1,4-DCN to 10 mg/L and 20 mg/L, respectively. The results showed that 98% removal could be achieved within 48 h at an initial 1,4-DCN concentration of 10 mg/L. Nevertheless, it took 144 h to reach the same degradation efficiency at an initial concentration of 20 mg/L. The degradation of 1,4-DCN may not remove the chloride ions during the processes and the metabolites may not benefit the bacterial growth. The research suggests a metabolic pathway of 1,4-DCN, which is critical for the treatment of this compound through biological processes.

Nitrification at full-scale municipal wastewater treatment plants: Evaluation of inhibition and bioaugmentation of nitrifiers.

Batch nitrification tests were conducted with sludge and wastewater streams obtained from field implementations to evaluate nitrification inhibition and efficiency of a nitrifiers bioaugmentation technology at full-scale municipal wastewater treatment plants (WWTPs). The results showed that the substrate organic carbon and pH of wastewater streams were inhibitory factors to nitrification and the low pH was the cause of the WWTP experiencing poor nitrification. An ammonia-nitrogen removal rate of 0.21mg-N/gMLVSS-h was observed at pH 6.5, while the rate increased to 0.54mg-N/gMLVSS-h with an introduction of 6% bioaugmented nitrifiers, indicating that the integrated side-stream nitrifiers bioaugmentation process was beneficial in improving nitrification efficiency, even under low pH conditions not conducive to nitrification. The study provides new insights into effective upgrading of municipal WWTPs exposed to poor nitrification.

Use of Bio-Amp, a commercial bio-additive for the treatment of grease trap wastewater containing fat, oil, and grease.

This research investigated the application of Bio-Amp, a commercial bio-additive for the treatment of fat, oil, and grease (FOG) in a grease trap, and evaluated potential impacts of treated effluent on downstream collection system and treatment processes. Results show that after Bio-Amp treatment, FOG deposit formation was reduced by 40%, implicating a potential reduction of sewer line blockages. Chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) and total fatty acids were reduced by 39%, 33%, 56%, and 59%, respectively, which represents an overall loading reduction of 9% COD, 5% TN and 40% TP received by the treatment plant from all the dining halls. On the other hand, readily biodegradable COD fractions significantly increased, which implies a potential improvement on Bio-P removal. Overall, the results showed that application of Bio-Amp in grease trap provides potential reduction of sewer line blockages, and can also alleviate downstream treatment burden.

Disinfection by-product formation potentials in wastewater effluents and their reductions in a wastewater treatment plant.

Disinfection by-product formation potentials (DBPFPs) in wastewater effluents from eight wastewater treatment plants (WWTPs) were investigated. In addition, a WWTP with one primary effluent and two different biological treatment processes was selected for a comparative study. Formation potential tests were carried out to determine the levels of DBP precursors in wastewater. WWTPs that achieved better organic matter removal and nitrification tended to result in lower DBPFPs in effluents. For the WWTP with two processes, haloacetic acid, trihalomethane, and chloral hydrate precursors were predominant DBP precursors in the primary and secondary effluents. The percent reductions of haloacetonitrile and haloketone formation potentials averaged at 96% which was high in comparison to the reductions of other classes of DBPFPs. In addition, biological treatment changed the DBPFP speciation profile by lowering the HAAFP/THMFP ratio. The eight plant survey and the comparative analysis of the WWTP with two processes implied that besides nitrification, there may be other confounding factors impacting DBPFPs. Oxic and anoxic conditions, formation and degradation of soluble microbial products had impacts on the DBPFP reductions. This information can be used by water and wastewater professionals to better control wastewater-derived DBPs in downstream potable water supplies.