Assessment of Sediment Arsenic and Iron Occurrence and Leaching Potential in a Potable Water Treatment Wastewater Stabilization Pond System

Wastewater stabilization ponds (WSPs) are commonly used to reduce wastewater metal(loid) concentrations from drinking water treatment plants (DWTPs) through sedimentation. However, this results in increased sediment concentrations that can be released back into the overlying water. Thus, our goal was to evaluate the WSP metal(loid)s occurrence and leaching potential. Currently, a Saskatchewan based DWTP’s WSP system was investigated given historically elevated effluent As and Fe concentrations. The WSP consists of five ponds that were sampled on six occasions in 2019 and 2020. In addition, sediments were used in laboratory-based experiments to determine their leaching potential. Overall, the sediments were found to contain elevated concentrations of As and Fe with 25 to 400 and 10,000 to 45,000 mg/kg, respectively. Leaching experiments indicated that the pond sediments could potentially release As and Fe with log Kd values ranging from 2.21 to 4.31 L/kg, while Fe ranged from 3.32 to 5.53 L/kg.

Identification of an Appropriate Formulation for Domestic Water Ceramic Filters from Soukamna Clay (Cameroon)

This paper deals with the formulation of ceramic filters having the porosity adapted to domestic potable water treatment. The filters were made from clays and rice husk obtained from the Far North region of Cameroon (Logone Valley). Nine formulations were investigated to choose those that might have the porosity standing between 35 and 50% (the ideal porosity adapted for water treatment) [1]. The nine formulations investigated were as follow: clay:rice husk mixture weight ratio 0.7:0.3; 0.8:0.2 and 0.9:0.1 with the particle size of 100:100 microns. The sintering temperatures of 900°C, 950°C and 1000°C were applied for each of the mixtures. The results showed that only filters with weight ratio 0.7:0.3 sintered at 900°C, 950°C and 1000°C had porosity between 35 and 50% with values of 39.41±0.96; 40.15±1.59; 40.14±1.31 respectively. Mechanical strength, permeability and iron leaching behavior were investigated for these three formulations. The formulation 0.7:0.3 with sintering temperature of 1000°C had the higher permeability and was the more stable for iron leaching so it is the more adapted for water treatment in terms of flow rate and iron leaching behavior, pore size distribution showed that these filters were macroporous and designed for microfiltration with average pore diameter of 0.46µm.

uMngeni Basin Water Quality Trend Analysis for River Health and Treatability Fitness

One of the main challenges facing the potable water production industry is deterioration of the quality of raw water. Drinking water that does not meet quality standards is unfit for consumption. Yet, this quality is a function of various factors, key among them being quality of the raw water from which it is processed. This is because costs related to potable water treatment are related to the nature of raw water pollutants and the degree of pollution. Additionally, survival of aquatic species depends on self-purification of the water bodies through attenuation of pollutants, therefore, if this process is not efficient it might result in dwindling of the aquatic life. Hence, this chapter presents spatial and temporal water quality trends along uMngeni Basin, a critical raw water source for KwaZulu-Natal Province, in South Africa. As at 2014 the basin served about 3.8 million people with potable water. Results from this study are discussed in relation to uMngeni River’s health status and fitness for production of potable water treatment. Time-series and box plots of 11 water quality variables that were monitored at six stations over a period of eight years (2005 to 2012), were drawn and analysed. The Mann Kendall Trend Test and the Sen’s Slope Estimator were employed to test and quantify the magnitude of the quality trends, respectively. Findings showed that raw water (untreated) along uMngeni River was unfit for drinking purposes mainly because of high levels of Escherichia coli. However, the observed monthly average dissolved oxygen of 7 mg/L, that was observed on all stations, suggests that the raw water still met acceptable guidelines for freshwater ecosystems. It was noted that algae and turbidity levels peaked during the wet season (November to April), and these values directly relate to chlorine and polymer dosages during potable water treatment.

Optimization of donnan dialysis for alum recovery from potable water treatment residues

Treatment of effluent water to meet fresh water discharge limits is very essential. Aluminium sulphate (alum) is the most widely used coagulant during the pre-treatment process, however, it generates a large amount of residue. Subsequent discharge of these residues from potable water treatment plants (PWTPs) to landfill sites and river bodies, without treatment, poses a great threat to the ecosystem and human health. In essence, the rising concern of managing residues, associated with the disposal cost, toxicity and stringent legislation, calls for more robust and effective technologies. In response, this study comes in handy owing to the green chemistry benefits of aluminium recovery from PWTPs for reuse. Primary recovery methods include acid treatment and alkalization. Although these two recovery processes ensue a minimum of 60% recovery, organics and heavy metals solubilize during the process. Donnan dialysis as a separation, recovery and concentrating technology is investigated in this project. The aims and objectives were to optimize the recovery of aluminium using Donnan dialysis with respect to phase conditions, to evaluate the inhibition effect of selected metals on aluminium transport and finally, to establish the organic transport in Donnan dialysis. Using a statistical approach, the feed phase conditions such as feed flowrate (0.64-2.21 mL/s), feed concentration (100-3300 mg/L), and pH (1.3-3.7) were considered against sweep phase conditions of acid concentration (0.25-1 N) and flowrate (0.64-2.21 mL/s). The response surface methodology’s face-centered central composite design (FC-CCD) statistical method was adapted for the selection of influential factors and establishing the relationship between selected conditions. The FC-CCD used had three levels and six center points for analysis. The effect of Ca, Mg, Mn, Fe, Cu, Zn and Pb on Al permeation through the Nafion 117 membrane was studied at constant flow and concentration conditions. Once the effects in the binary inhibition study were completed, aluminium recovery from a residue obtained from a local PWTP was conducted. Simultaneously, the rejection of organics by the membrane was also assessed during the aluminium recovery process. Preliminary experiment validation experiments showed a high deviation of ±6.4 mg/L at the feed phase, 7.33% deviation at the sweep phase and mass balance closure greater than 95%. Furthermore, study on the water transport across the membrane was directly proportional to the acid concentration. Comparing HCl and H2SO4, HCl had a lower Van’t Hoff factor, hence, was used in proceeding experiments. A one factor at a time experiment to determine the final range of feed concentration to use showed that a maximum of 2000 mg/L was required to meet a 50% recovery target. The FC-CCD experiment showed that the ascending order of the effects of factors was sweep flowrate < feed flowrate < sweep concentration < feed concentration. The sweep flowrate had a negative influence on aluminium permeation and was statistically insignificant (p > 0.05). Quadratic and predictive models developed at different time intervals were statistically significant at a 95% confidence level. Also, a high recovery of 94% and high concentrating effect at the sweep phase was 1.65 in the 2:1 feed to sweep phase volume experiment. Analysis of FC-CCD combinative study of feed concentration, pH of feed phase and feed flowrate showed that a high feed concentration (> 1000 mg/L) at a high pH (> 2.5) will yield an Al-recovery > 60%. At a 95% confidence level, the statistical analysis showed that the pH was the most significant factor. The interacting factors for the statistically significant model was feed concentration-feed flowrate and feed concentration-pH. The one-on-one inhibitive study at equal phase flowrates and feed concentration revealed that Fe gave the highest inhibition while the least transport across the Nafion 117 membrane was Mn2+. In descending order, Fe2+ > Ca2+ > Zn2+ > Mg2+ > Cu2+ . The rejection of organics is limited to 24- 32 hours where a maximum of 98% rejection was achieved under the synthetized solution and acid digested residue runs. In conclusion, Donnan dialysis by RSM has proven to be feasible for the recovery of aluminium from potable water treatment residue. Also, the FC-CCD adapted from the RSM is seen to be very promising, economical and a reliable alternative statistical tool to determine the most influential factor and predict and obtain the optimal operation conditions for a system. Therefore, there are economic, sustainable and research prospects of DD coupled with RSM towards recovery of metal salts and heavy metals from PWTP residues in large scale implementation.

ANALYSIS OF TECHNICAL SOLUTIONS FOR SHIP POTABLE WATER SYSTEMS

The article provides an overview and analysis of all main types of potable water systems currently used on inland and mixed navigation vessels: without potable water treatment; with elements of potable water disinfection and conditioning; with complete purification and disinfection of potable water. The operation principles of potable water systems of all types and designs are considered in detail, all the advantages and disadvantages of these systems are noted. Special attention is paid to stations for preparing potable water by using UV lamps, which essentially differ in the technological process from most of the stations used, and provide guaranteed high-quality disinfection of potable water, which allows to choose the most promising station type and outline a plan for further work on creating new and improving existing stations.

A new backwash strategy for reducing the cost of an immersed ultrafiltration system by restricting cake layer breakage

Ultrafiltration (UF) is increasingly used for potable water treatment, but membrane fouling necessitates the application of periodical backwash, which increases running cost. A new backwash strategy, in which air scouring was only applied with sludge water discharging, was proposed to improve backwash performance in a water plant using UF. Four gravity-driven UF systems were simultaneously run at increasing air scouring intervals (3–24hours) and sludge water discharging intervals (12–24hours). The membrane fluxes were monitored to assess membrane fouling and the mix solution turbidity was also monitored to investigate deposition of particles. The results indicated that membrane fouling was not aggravated by the extension of air scouring and sludge water discharging intervals. Water backwash on its own induced a shift of particle deposition from the membrane surface to the bottom of the membrane tank due to limited cake layer breakage, enabling the extension of sludge water discharging intervals. For the gravity-driven system investigated, the running cost, including energy, water and chemical demand, was reduced by 16.67% as the air scouring and sludge water discharging intervals increased from 3hours to 24hours and from 12hours to 24hours, respectively.