A systematic review of the water treatment sludge toxicity to terrestrial and aquatic biota: state of the art and management challenges.

Safe drinking water' supply is an essential service and depends directly on the water treatment that produces water treatment sludge (WTS) as a product, whose final destination varies and remains a challenge. The ecotoxicity assessment of the WTS address the ecological implications of the WTS disposal but these information is still scarce in the literature. In this sense, we did a systematic review of the ecotoxicological studies on WTS using databases from six platforms. From the 785 papers recovered; 16 studies were eligible and showed the ecotoxicity assays' applicability to evaluate the WTS. We discussed WTS ecotoxicity considering sample characterization; terrestrial and aquatic toxicity assays; and WTS challenges. WTS proved to be a highly heterogeneous matrix composed mainly of coagulant precipitates, including Al and Fe. Studies lack consensus concerning the most representative/sensitive species for evaluating WTS' toxicity. Crustaceans were the most studied aquatic group, although algae species were more sensitive. Besides, soil ecotoxicity assessed only plant growth, and a single study used the earthworm. Even papers used bioassays to indicate the recycling WTS' feasibility, there is a lack of specific legislation regarding the WTS reuse. Furthermore, are necessary a regulation for WTS management that involves an ecological risk assessment.

Filter media depth and its effect on the efficiency of Household Slow Sand Filter in continuous flow.

This study evaluated the impact of a 50% reduction of filter media depth in Household Slow Sand Filters (HSSFs) on continuous flow to remove physicochemical and microbiological parameters from river water. Furthermore, simple pre-treatment and disinfection processes were evaluated as additional treatments. Two filter models with different filtration layer depths were evaluated: a traditional one with 50 cm media depth (T-HSSF) and a compact one (C-HSSF) with 25 cm. HSSFs were fed with pre-treated river water (24-h water sedimentation followed by synthetic fabric filtration) for 436 days at a constant filtration rate of 0.90 m3 m-2 day-1 with a daily production of 48 L day-1. Sodium hypochlorite (2.0 mg L-1 of NaOCl 2.5% for 30 min) was used to disinfect the filtered water. Water samples were analysed weekly for parameters such as turbidity, organic matter, colour and E. coli, among others. Removal of protozoan cysts and oocysts by the HSSFs were also evaluated. After pretreatment, turbidity from the HSSF river water was reduced to 13.2 ± 14.6 NTU, allowing the filters to operate. Statistical analysis indicated no significant difference (p > 0.05) between T-HSSF and C-HSSF efficiencies in all evaluated parameters throughout operation time. Hence, media depth reduction did not hinder continuous HSSF performance for almost all the evaluated parameters. However, it may have affected Giardia cysts retaining, which passed through the thinner media on one evaluation day. Disinfection was effective in reducing remaining bacteria from filtered water; however, it was ineffective to inactivate protozoa. The reduction in the filtration layer did not affect the overall filtered water quality or quantity showing that a compact HSSF model may be a viable option for decentralized water treatment.

Evaluation of a multi-barrier household system as an alternative to surface water treatment with microbiological risks.

Household Water Treatment and Safe Storage (HWTS) are recommended to supply the demand for drinking water in communities without conventional water supply systems. However, there is a lack of long-term laboratory studies regarding such technologies. We evaluated the contributions of each step of a multi-barrier system with pretreatment (sedimentation and fabric filtration), filtration in Household Slow Sand Filters (HSSFs) and disinfection (sodium hypochlorite) treating surface water for more than 14 consecutive months. Removal of turbidity, colour, organic matter, coliform group bacteria and protozoa were evaluated. Two HSSF models were compared, one with a diffuser vessel (HSSF-d) and one with a gravity float equipped vessel (HSSF-f). Correlations between efficiency and operational parameters were assessed. Overall, the multi-barrier system removed more than 90% of turbidity and more than 3.5 log of Escherichia coli. HSSF removed up to 3.0 log of Giardia spp. and 2.4 log of Cryptosporidium spp. HSSF-f presented significantly higher removal rates for turbidity, apparent colour and E. coli. Disinfection resulted in water with E. coli concentration lower than 1 CFU 100mL-1, however it was not able to inactivate protozoa. The evaluated system was able to reduce microbiological risks from water and could indeed be an alternative to communities that depend on surface water as their main source of supply. Nevertheless, further studies are recommended to include a low-cost disinfectant for protozoa inactivation.

Household slow sand filters in continuous and intermittent flows and their efficiency in microorganism's removal from river water.

This study aimed to evaluate the efficiency of four household slow sand filter (HSSF) models for the removal of microorganisms from river water throughout the development of their biological layers (schmutzdecke). Two models were designed to be operated continuously (HSSF-CC and HSSF-CT) and two intermittently (HSSF-ID and HSSF-IF). Filters were fed daily with 48 L pre-treated river water (24 h sedimentation followed by filtration through a non-woven synthetic blanket). Water samples were quantified by coliform group bacteria and analysed by bright field microscopy to visualize the microorganisms. Total coliform reduction was between 1.42 ± 0.59 log and 2.96 ± 0.58 log, with continuous models showing a better performance (p-values < 0.004). Escherichia coli reduction varied from 1.49 ± 0.58 log to 2.09 ± 0.66 log and HSSF-IF, HSSF-CC and HSSF-CT presented a similar performance (p-values > 0.06), slightly better than the one presented by HSSF-ID (p-value=0.04). Microorganisms, such as algae, protozoa and helminths were detected by microscopy in raw water and pre-treated water. Algae were the most significant group in these samples, although they were not visualized by bright field microscopy in the filtered water. Results showed the potential of HSSF in microbiological risk reduction from river water, which increases the range of point-of-use water treatments in rural communities. However, additional studies of the HSSF biological layer must be performed.