Slow Sand Filters for the 21st Century: A Review

Synthesis, characterization, and environmental applications of graphene-coated sand: A review

Global water quality has deteriorated, leaving over 844 million individuals without access to clean drinking water. While sand filters (SF) offer a solution, their limited surface area and adsorption capacity for emerging contaminants remain a challenge. This has prompted the development of new materials such as graphene-coated sand (GCS) to enhance the sand's adsorptive properties. Notably, GCS also possesses inherent anti-bacterial properties and can function as a photocatalyst when exposed to UV and visible light, offering enhanced water purification. This manuscript 1) reviews the synthesis of GCS, detailing the characterization techniques employed to understand its structure, composition, and multifunctional properties and 2) highlights the superior efficacy of GCS in removing contaminants, including metals (>95 % removal of Cd2+, Pb2+, Zn2+, and Cu2+ in low pH environment), sulfides (full removal compared to 26 % removal by raw sand), antibiotics (98 % removal of tetracycline), and bacteria (complete cell membrane destruction), compared to traditional SF. Due to its enhanced performance and multifaceted purification capabilities, GCS presents a promising alternative to SFs, especially in developing countries, aiming to improve water quality and ensure safe drinking water access. To the best of our knowledge, no other work groups the available research on GCS. Furthermore, future research directions should focus on reducing the overall production cost of GCS, exploring surface modification techniques, and expanding the range of contaminants tested by GCS, to fully realize its potential in water purification.

Safeguarding drinking water: A brief insight on characteristics, treatments and risk assessment of contamination

Water pollution stands as a critical worldwide concern, bearing extensive repercussions that extend to human health and the natural ecosystem. The sources of water pollution can be diverse, arising from natural processes and human activities and the pollutants may range from chemical and biological agents to physical and radiological contaminants. The contamination of water disrupts the natural functioning of the system, leading to both immediate and prolonged health problems. Various technologies and procedures, ranging from conventional to advanced, have been developed to eliminate water impurities, with the choice depending on the type and level of contamination. Assessing risks is a crucial element in guaranteeing the safety of drinking water. Till now, research is continuing the removal of contaminates for the sake of supplying safe drinking water. The study examined physical, inorganic, organic, biological and radiological contaminants in drinking water. It looked at where these contaminants come from, their characteristics, the impact they have and successful methods used in real-world situations to clean the contaminated water. Risk assessment methodologies associated with the use of unsafe drinking water as future directives are also taken into consideration in the present study for the benefit of public concern. The manuscript introduces a comprehensive study on water pollution, focusing on assessing and mitigating risks associated with physical, inorganic, organic, biological and radiological contaminants in drinking water, with a novel emphasis on future directives and sustainable solutions for public safety.

Performance of a modified and intermittently operated slow sand filter with two different mediums in removing turbidity, ammonia, and phosphate with varying acclimatization periods

The present study investigated the utilization of blood clam shells as a potential substitute for conventional media, as well as the influence of the acclimation time on the efficacy of an intermittent slow sand filter (ISSF) in the treatment of real domestic wastewater. ISSF was operated with 16 h on and 8 h off, focusing on the parameters of turbidity, ammonia, and phosphate. Two media combinations (only blood clam shells [CC] and sand + blood clam shells [SC]) were operated under two different acclimatization periods (14 and 28 d). Results showed that SC medium exhibited significantly higher removal of turbidity (p < 0.05) as compared to CC medium (45.99 ± 26.84 % vs. 3.79 ± 9.35 %), while CC exhibited slightly higher (p > 0.05) removal of ammonia (23.12 ± 20.2 % vs. 16.77 ± 16.8 %) and phosphate (18.03 ± 11.96 % vs 13.48 ± 12 %). Comparing the acclimatization periods, the 28 d of acclimatization period showed higher overall performances than the 14 d. Further optimizations need to be conducted to obtain an effluent value below the national permissible limit, since the ammonia and phosphate parameters are still slightly higher. SEM analysis confirmed the formation of biofilm on both mediums after 28 d of acclimatization; with further analysis of schmutzdecke formation need to be carried out to enrich the results.