Water quality indices appraisal and health risk assessment of nitrate,mercury and lead in water distribution network: A case study of Robat Karim in Tehran,Iran

Groundwater is a basic source of drinking water supply for urban and rural areas. This is especially the case for communities located in arid and semi-arid regions that rely on groundwater for drinking purposes. The present study set out to assess the potential health impacts of water impurities and to investigate the qualitative status of drinking water in Robat Karim rural areas, located in southwest Tehran, Iran. A total of 66 samples were collected from the water distribution network of 11 villages (33 sampling points, on two occasions) during September 2020 and were tested in terms of the most common quality parameters such as pH, mercury (Hg), lead (Pb), copper (Cu), zinc (Zn), chloride (Cl^–), chlorate (ClO₃^–), nitrite (NO₂^–), nitrate (NO₃^–), and flouride (F^–). Multiple methods and indexes including water quality index (WQI), hazard quotient (HQ), and hazard index (HI), were worked out to assess the quality of water and health risk assessment of NO₃^– Pb²⁺ and Hg²⁺. The results revealed that 33% and 90% of sampling sites have significantly high nitrate and total hardness (TH) concentrations, exceeding the maximum permissible limits set by World Health Organization (WHO; 50 and 200 mg/L, respectively). Furthermore, five sampling points exhibited poor WQIs mainly related to NO₃^– and TH. HQ values higher than 1 for nitrate were noticed in most sampling locations. Except for one sampling point, the HQ obtained for Pb²⁺ and Hg²⁺ were below 1 indicating no obvious health hazard. This study represents that children and infants are at higher risk of chronic toxicity by excess NO₃^– intake. The health hazard that is yet imposed on the community by NO₃^– necessitates regular monitoring of drinking water, the use of advanced technologies to purify water or otherwise alternative resources should be proposed.     

Evaluating two test methods used for characterizing leaching properties

A standard leaching test method (EN 12457-3) was compared with a modified pHstat-column leaching test method with respect to leaching information obtained for aggregates composed of different alkaline solid wastes. In addition to a different experimental set-up, the major dissimilarity between the two test methods was the chemical equilibrium condition, i.e., in the first test the system approaches equilibrium while in the second test the system is far from equilibrium conditions. The leaching trends of sodium, calcium, chloride, sulfate and cadmium were studied. Results showed that these two test methods were comparable in respect to the total amount sodium and sulfate leached. It was also concluded that the two test methods provide different information for the constituents for which dissolution reaction is highly dependent on pH and other experimental conditions, e.g., flow rate. It was found that a batch test can be used in order to investigate the total amount leached, while a modified column-pHstat test generates more detailed results on leaching trends of some constituents.     

Low-energy sodium hydroxide recovery for CO2 capture from atmospheric air—Thermodynamic analysis

To reduce the risks of climate change, atmospheric concentrations of greenhouse gases must be lowered. Direct capture of CO₂ from ambient air, “air capture”, might be one of the few methods capable of systematically managing dispersed emissions. The most commonly proposed method for air capture is a wet scrubbing technique which absorbs CO₂ in an alkaline absorbent, i.e. sodium hydroxide producing an aqueous solution of sodium hydroxide and sodium carbonate. In most of the previous works it was assumed that the absorbent would be regenerated and CO₂ liberated from the alkaline carbonate solution using a lime and calcium carbonate causticization cycle.We describe a novel technique for recovering sodium hydroxide from an aqueous alkaline solution of sodium carbonate and present an end-to-end energy and exergy analysis. In the first step of the recovery process, anhydrous sodium carbonate is separated from the concentrated sodium hydroxide solution using a two-step precipitation and crystallization process. The anhydrous sodium carbonate is then causticized using sodium tri-titanate. The titanate direct causticization process has been of interest for the pulp and paper industry and has been tested at lab- and pilot-scale. In the causticization process, sodium hydroxide is regenerated and carbon dioxide is liberated as a pure stream, which is compressed for use or disposal. The technique requires ～50% less high-grade heat than conventional causticization and the maximum temperature required is reduced by at least 50 °C. This titanate cycle may allow a substantial reduction in the overall cost of direct air capture.     

Benzene degradation in waste gas by photolysis and photolysis-ozonation: experiments and modeling

A photochemical model of benzene degradation compares well with experimental data obtained in the Lab. 62 reactions were needed to fully describe benzene degradation. A feasibility study shows that the photolysis of benzene is a cost-effective process. Experimental data and modeling results show that the degradation efficiency will increase when the combination of UV light and ozone is used. The degradation of benzene, a carcinogenic air pollutant, was studied in a gas-phase photochemical reactor with an amalgam lamp emitting ultraviolet light at 185 and 254 nm. Efficient benzene degradation (>70%) was possible for benzene mass flow rates of up to 1.5 mg·min⁻¹. Adding ozone allowed benzene mass flow rates of up to 5 mg·min⁻¹ to be treated with the same efficiency. In terms of energy consumption, ozone doubles the efficiency of the process. A comprehensive mechanistic simulation model was developed incorporating a chemical kinetics model (62 reactions involving 47 chemical species), a material balance model incorporating diffusion and flow, a flow velocity model, and a light field model. The model successfully predicted the efficiency of the reactor, generally within 20%, which indicates that the model is sound, and can be used for feasibility studies. The prediction of the reactor efficiency in the presence of ozone was less successful, with systematically overestimated efficiency. Condensation of reaction products in the reactor is thought to be the main cause of model inaccuracy. Both experimental data and model predictions show that there is a synergistic effect between ozonation and ultraviolet degradation.