Impacts of backwashing on micropollutant removal and associated microbial assembly processes in sand filters

Backwashing is crucial for preventing clogging of sand filters.However,few studies have investigated the effect of backwashing on micropollutant removal and the dynamic changes in the microbial community in sand filters.Here,we used a series of manganese and quartz sand filters under empty bed contact times(EBCTs)of 2 h and 4 h to explore variations in micropollutant degradation and temporal dynamics of the microbial community after backwashing.The results showed that the removal efficiencies of caffeine,sulfamethoxazole,sulfadiazine,trimethoprim,atrazine,and active biomass recovered within 2 d after backwashing in both types of sand filters at 2-h EBCT,but the recovery of sulfadiazine and trimethoprim was not observed at 4-h EBCT.Moreover,the removal efficiency of atenolol increased after backwashing in the manganese sand filters,whereas maintained almost complete removal efficiency in the quartz sand filters at both EBCTs.Pearson correlation analysis indicated that microbial community composition gradually recovered to the pre-backwashing level(R increased from 0.53 to 0.97)at 2-h EBCT,but shifted at 4-h EBCT(R<0.25)after backwashing.Furthermore,the compositions of the recovered,depleted,and improved groups of microbes were distinguished by applying hierarchical clustering to the differentially abundant amplicon sequence variants.The cumulative relative abundance of recovered microbes at 2-h EBCT was 82.76%±0.43%and 46.82%±4.34%in the manganese and quartz sand filters,respectively.In contrast,at 4-h EBCT,the recovered microbes dropped to 15.55%–25.69%in both types of sand filters.

Irrigation of Romaine Lettuce (Lactuca sativa)Using Wastewater Treated byNon-Conventional Technologies

The aim of this study was to assess the capacity for reuse of wastewater treated in stabilisation ponds and subsequently reclaimed by means of different filtration systems at pilot scale. An analysis of filtered water showed turbidity values of below 5 NTU, a total suspended solids (TSS) content of 7 mg/l, and Escherichia coli values of up to 1.6 log CFU/100 ml. These results fall within the parameters stipulated in RD 1620/2007 Spanish Water Reuse Regulations governing the reuse of reclaimed wastewater for agricultural purposes. The water reclaimed by means of filtration systems was used to irrigate Romainelettuce (Lactuca sativa longifolia), comparing growth with that of the same variety irrigated with water from the supply network. The results showed a mean difference in lettuce growth of up to 300% in favour of the crop irrigated with reclaimed water.

Comparing unamended and Fe-coated biochar on removal efficiency of bacteria,microspheres,and dissolved phosphorus in sand filters

The effects of uncoated and Fe-coated biochars(BC)on the removal of bacteria,microspheres,and dissolved reactive phosphorus(DRP)in sand filters were compared.Filters were packed with 1.2 or 2.0-mm sand mixed with 30%(vol/vol)uncoated BC,Fe-coated BC,or a control without BC.Removal of E.coli,Salmonella,and Enterococci increased from 23,42,and 25%in the unamended 1.2-mm sand to 48,80,and 75%in the uncoated BC treatment,though only the increase for Enterococci was significant(p<0.05).For the Fe-coated BC,removal efficiencies were 89,93,and 94%,respectively,which were all significantly(p<0.05)greater than the unamended sand but only the removal of E.coli was significantly greater than the uncoated BC sand filter.For the 2.0-mm sands,the only significant increase in removal following BC addition was observed for Salmonella.Trends in microsphere removal were generally consistent with bacteria.Removal of DRP in the unamended and uncoated BC filters was 33 and 13%(p>0.05),respectively,whereas removal in the Fe-coated BC filters was 98%(p<0.05).Results from batch sorption experiments indicate that both BCs similarly increased bacterial sorption to sand.In contrast,DRP sorption to the unamended and uncoated BC-amended sands were similar(p>0.05)with DRP sorption to the Fe-coated BC-amended sand being significantly greater(p<0.05).Results indicate that Fe-coated BC is more effective at retaining DRP than bacteria and microspheres in sand filters.

Role of sand size on bacterial retention in biochar-amended sand filters

The addition of biochar to sand columns can enhance the retention of bacteria and thus may provide a management strategy for removing bacteria from tile-drainage waters.In this study,the role of sand size as a factor in controlling microbial reten-tion in biochar-amended sand columns was investigated.Laboratory column experiments were conducted to quantify the removal of two bacterial isolates(E.coli and Salmonella)and polystyrene microspheres in 10-cm-long columns packed with clean sand of three different sizes(0.25,0.71,and 1.19 mm)at four biochar concentrations(0%,5%,10%,and 15%).Sorption studies were also performed to help identify the relative roles of sorption and physical straining on the removal of bacteria and microspheres within the columns.For the large sand,the log10 removal values(LRV)for E.coli increased from 0.22 to 0.49 for the 0%and 15%biochar concentrations,respectively,while LRV for Salmonella increased from 0.19 to 0.68.For the small sand,increasing biochar concentration from 0%to 15%increased LRV from 0.11 to 1.9 for E.coli and from 0.20 to 4.6 for Salmonella.In comparison,LRV for microspheres in the 15%biochar columns was only minimally higher than the unamended columns for all three sand sizes.Results from the sorption studies show that high sorption coefficients generally correlated with high LRV indicating that sorption rather than physical straining was the primary mechanism of retention in the columns.Results from this study further our understanding of bacterial retention in biochar-amended porous media.