Role of Carbonate Species on General Acid Catalysis of Bromide Oxidation by Hypochlorous Acid (HOCl) and Oxidation by Molecular Chlorine (Cl2).

Kinetic models for disinfectant decay and disinfection byproduct (DBP) formation are necessary for predicting water quality from the treatment plant to the tap. A kinetic model for conditions relevant to chloramine disinfection of drinking water (pH 6-9 and carbonate-buffered) was developed to simulate incomplete bromide (Br-) oxidation during short prechlorination periods because it is the first step in a complex system of reactions that leads to disinfectant loss and DBP formation. Hypochlorous acid (HOCl+Br-→kHOClHOBr+Cl-) and molecular chlorine (Cl2+Br-+H2O→kCl2HOBr+2Cl-+H+) were the free chlorine species relevant to Br- oxidation, and Cl2 hydrolysis and formation reactions (Cl2+H2O+A-⇌k-4k4HOCl+HA+Cl-) were necessary to accurately simulate Cl2 concentrations instead of assuming equilibrium. Previous work has shown that Br- oxidation by HOCl and Cl2 formation are acid-catalyzed and Cl2 hydrolysis is base-catalyzed, but the impact of carbonate species had not been studied. This work showed that the carbonate species have an enhanced catalytic impact with rate constants up to 1000 times larger than would be estimated by the Brønsted relationship for similar acids, which causes the oxidation by HOCl rate constant (kHOCl) to nearly double and oxidation by Cl2 to occur above pH 7 in high-alkalinity waters.

Treatment and potential reuse of greywater from schools: a pilot study.

This study presented performance data on a low cost and easy maintenance pilot system for on-site treatment and reuse of water collected from wash sinks and fountains, as major sources of greywater (GW) at schools. Various treatment options were studied including screening, sand filtration, chlorination, and UV disinfection operated at different flow rates. Results showed that filtration operated at low rates is very effective in total suspended solids (TSS) removal, while UV proved to be more effective than chlorination for reduction of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total coliforms. Removal efficiencies up to 63%, 30% and 20% were obtained for TSS, COD and BOD, respectively and reductions of log TC (CFU/100 ml) from 6.5 to 2 were obtained at a filtration rate of 14 m3/d·m2. Treated effluent satisfied WHO standards for reclaimed water reuse in landscape irrigation and toilet flushing. The filtration-UV system is robust, showing the best and most reliable performance for low and high strength GW treatment even under a 10-fold increase in flow rate. A 5 m3/d pilot plant was developed for schools having 500 students and detailed cost-benefit analysis indicated a net saving value, a surplus of $1,600 per year, and pay back after 6 years and 11 months.

Quantification and characterization of greywater from schools.

Survey of schools of different education levels (primary, intermediate and secondary) in Kuwait showed an average greywater generation rate of 7.3 L/p/d and varied in the range of 2.9-16 l/p/d, reflecting the school level of education (i.e. student age). The highest rates were observed for primary schools while the lowest rates were observed in secondary schools where students are more mature and use the water more wisely. The greywater characteristics indicated waste with low chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5) values but relatively high solids, conductivity, and sodium content due to excessive use of hand soap. Total coliform values ranged between 89 and 352 most probable number (MPN)/mL with an average of 196 MPN/mL while no fecal coliform values were detected. Greywater collected from schools is classified as light greywater and contains much lower levels of organic matter and nutrients compared to residential greywater and domestic wastewater. It is suitable for non-potable reuse after minimal treatment since microbial contamination may pose a serious threat to health if greywater comes into contact with humans. It also provides a good opportunity for reuse in toilet flushing since it can be easily collected from wash sinks and fountains, as major sources, and recycled.

Adsorption capacity of activated carbon derived from date seeds: Characterization, optimization, kinetic and equilibrium studies.

Agricultural wastes have the potential to be reused in applications such as water/wastewater treatment. Several studies have focused on activating organic waste, such as date seeds, to produce activated carbon. However, these studies have always assumed that all date seeds behave similarly to each other. In this study, we evaluated different types of date seeds and characterized their physical-chemical properties. The results showed variation in the seed-to-fruit weight percentage, ash content, and moisture content among different seed types. Different activation procedures were performed to find the optimum combination of physical and chemical interventions. KOH impregnation yielded better results than H3PO4 impregnation. The maximum adsorption capacity was measured for nine different types of date seeds, and the Khalas seed type yielded the highest methylene blue (MB) adsorption capacity of 165 mg of MB/g of activated date seeds (ADS), which is 71% of the capacity of commercial activated carbon (CAC). Kinetics model was fitted to the experimental data, and the pseudo-second-order model provided the best fit, indicating that the adsorption process occurred following a chemical process rather than being controlled by intraparticle diffusion only. The results showed no significant difference among the three isotherm models used to fit the experimental data. The results indicated that there is a significant difference among various types of seeds regarding adsorption performance. The application of ADS in treating synthetic produced water showed that its performance is one third that of CAC. ADS showed promising potential in comparison with CAC, mostly considering the costs involved with CAC.

Recirculating treated sewage sludge for agricultural use: Life cycle assessment for a circular economy.

The objective of this study is to assess the environmental value of recirculating nutrients from treated sewage sludge by application to agricultural soils to grow forage as opposed to landfilling and incineration. The methodological choices are aligned to the circular economy framework using life cycle assessment. Consequential modeling and open loop modeling were adopted and adhere to ISO 14044 and International Reference Life Cycle Data System (ILCD) standards. The functional unit is defined in terms of the amounts of nitrogen (N), phosphorus (P) and potassium (K) recirculated from the treated sewage sludge produced annually in Kuwait. The results indicate a reduction in environmental burden with respect to fossil fuel depletion, metal depletion and climate change. A total of 95% of the reduction is realized by avoiding virgin nitrogen production and instead using its recirculated counterpart. Considerable amounts of natural gas, coal, dinitrogen monoxide (nitrous oxide, N2O) and copper are consumed during virgin N fertilizer production.

Assessment of grate sag inlets in a residential area based on return period and clogging factor.

Storm in-sag inlets, which typically have inflow capture efficiency of 100%, can violate the allowable water spread criterion of roadways, thus slowing the traffic movement and contributing to accidents. This is especially evident during severe storms of high return periods and when a storm sewer inlet of grate type is adopted, because it is subject to debris and trash clogging factors. In this study, the water spread on pavement for in-sag grates located in a residential area in Kuwait is analyzed in terms of return period and clogging factor. It is found that for a single grate inlet with a return period of 10 years, a clogging factor of 50% can lead to a water spread value exceeding the local design constraint assigned for residential areas, which is one traffic lane of 4m width. It is also shown that for in-sag locations, a double-grate inlet is more preferable than the single one, because the former tends to reduce the adverse hydraulic effect of total inflow on water spread width. The effect of clogging factor on a multiple-grate inlet located in sag is determined from a simple expression suggested in this study.