Spatial and temporal changes in Actinobacterial dominance in experimental artificial groundwater recharge

Artificial groundwater recharge (AGR) is used in the drinking water industry to supplement groundwater resources and to minimise the use of chemicals in water treatment. This study analysed the spatial and temporal changes of microbial communities in AGR using two test systems: a nutrient-amended fluidized-bed reactor (FBR) and a sand column. Structural changes in the feed lake water (Lake Roine), FBR, and sand column bacterial communities were determined by denaturing gradient gel electrophoresis (DGGE) and the length heterogeneity analysis of amplified 16S rRNA genes (LH-PCR). Two clone libraries were created to link the LH-PCR results to the dominant bacterial groups. The lake water bacterial community was relatively stable, with three bands dominating in all LH-PCR products. The most dominant fragment accounted for up to 72% and was derived from Actinobacteria. Based on the clone libraries and LH-PCR data, Actinobacteria also dominated in the unattached bacterial community of the FBR, whereas several Proteobacterial groups were more abundant on the FBR carrier particles. In the stabilised AGR system a major change in the community structure of the lake water bacteria took place during passage within the first 0.6 m in the sand column as the community composition shifted from Actinobacteria-dominated populations to a diverse, mainly Proteobacterial communities. Concurrently, most of the dissolved organic carbon (DOC) was removed at this stage. In summary, the study showed that the make-up of microbial communities in experimental AGR systems responded to changes in their environment. LH-PCR showed potential as a method to determine microbial community dynamics in long-term studies at real-scale AGR sites. This is the first step to provide data on microbial community dynamics in AGR for drinking water production.     

Extracellular enzyme activities and nutrient availability during artificial groundwater recharge

Natural organic matter (NOM) removal is the main objective of artificial groundwater recharge (AGR) for drinking water production and biodegradation plays a substantial role in this process. This study focused on the biodegradation of NOM and nutrient availability for microorganisms in AGR by the determination of extracellular enzyme activities (EEAs) and nutrient concentrations along a flow path in an AGR aquifer (Tuusula Water Works, Finland). Natural groundwater in the same area but outside the influence of recharge was used as a reference. Determination of the specific α-d-glucosidase (α-Glu), β-d-glucosidase (β-Glu), phosphomonoesterase (PME), leucine aminopeptidase (LAP) and acetate esterase (AEST) activities by fluorogenic model substrates revealed major increases in the enzymatic hydrolysis rates in the aquifer within a 10 m distance from the basin. The changes in the EEAs along the flow path occurred simultaneously with decreases in nutrient concentrations. The results support the assumption that the synthesis of extracellular enzymes in aquatic environments is up and down regulated by nutrient availability. The EEAs in the basin sediment and pore water samples (down to 10 cm) were in the same order of magnitude as in the basin water, suggesting similar nutritional conditions. Phosphorus was likely to be the limiting nutrient at this particular AGR site. Furthermore, the extracellular enzymes functioned in a synergistic and cooperative way.     

Changes in dissolved organic carbon during artificial recharge of groundwater in a forested esker in Southern Finland

Sprinkling infiltration in a forested esker leading to artificial recharge of groundwater was studied in Southern Finland. Changes in dissolved organic carbon (DOC) and the molecular size distribution and chemical properties of the organic carbon were investigated during the infiltration process. Artificial groundwater was produced using sprinkling infiltration directly onto the forest floor. One result of lake water infiltration through the organic horizon and 1 m thick mineral soil layer was a slight net increase in the DOC concentrations from 9.4 mg/L in the infiltration water to 13.2 mg/L in percolation water. This indicates that the forest soil represents a potential input of organic matter into infiltration water. However, the DOC concentrations decreased by 27–38% as the infiltration water percolated down through the unsaturated soil layer into the groundwater zone. At a distance of 1450 m from the infiltration area, the mean DOC concentration in the groundwater was below the recommended value for drinking water in Finland of 2.0 mg/L. There was a strong reduction in the concentrations of hydrophilic and hydrophobic acids, but only a slight decrease in hydrophilic neutral organic compounds during the infiltration process. The DOC in the production well consisted of low molecular size fractions. Larger molecular size fractions were removed effectively from the water during the infiltration process.     

Using soil biomass as an indicator for the biological removal of effluent-derived organic carbon during soil infiltration

This study investigates the relationship between soil biomass and organic carbon removal during the infiltration of conventionally treated effluents used for groundwater recharge during soil-aquifer treatment (SAT). Investigations were conducted on samples collected from full-scale SAT sites, revealing a positive correlation between biodegradable organic carbon (BOC) concentrations in the recharged effluents and total viable soil biomass concentrations in the infiltration zone of soil samples collected from respective recharge basins. Findings of this study suggest that BOC limits soil biomass growth and was able to support a steady-state concentration of viable soil biomass that is characteristic to BOC concentrations introduced with the recharged effluents. All investigated sites indicate that BOC is primarily removed within 30 cm soil depth leading to a significant increase in soil biomass levels (measured as substrate induced respiration (SIR), total viable biomass, and dehydrogenase activity (DHA)). Controlled biological column studies revealed that the primary components of BOC in domestic effluents are organic colloids. Findings of this study support that hydrophobic acids, commonly believed to be recalcitrant, may also be attenuated by biological processes during soil infiltration.     

云冈石窟入渗水的形成和运移

在云冈石窟地区,大气降水的入渗不仅是地下水的补给来源,也是洞窟石壁表面水分的来源之一。夏季强降雨和春季融雪是研究区入渗水产生的重要途径。石窟山体包气带厚,入渗水需要经过多层介质才能补给地下水,以石窟围岩中发育的2组优势垂直裂隙为主要运移通道。采用多种方法进行综合分析,估算出降水入渗系数为2.6%～5.4%,平均入渗强度为10～20mm/a。     

Managed aquifer recharge of treated wastewater: water quality changes resulting from infiltration through the vadose zone

Secondary treated wastewater was infiltrated through a 9 m-thick calcareous vadose zone during a 39 month managed aquifer recharge (MAR) field trial to determine potential improvements in the recycled water quality. The water quality improvements of the recycled water were based on changes in the chemistry and microbiology of (i) the recycled water prior to infiltration relative to (ii) groundwater immediately down-gradient from the infiltration gallery. Changes in the average concentrations of several constituents in the recycled water were identified with reductions of 30% for phosphorous, 66% for fluoride, 62% for iron and 51% for total organic carbon when the secondary treated wastewater was infiltrated at an applied rate of 17.5 L per minute with a residence time of approximately four days in the vadose zone and less than two days in the aquifer. Reductions were also noted for oxazepam and temazepam among the pharmaceuticals tested and for a range of microbial pathogens, but reductions were harder to quantify as their magnitudes varied over time. Total nitrogen and carbamazepine persisted in groundwater down-gradient from the infiltration galleries. Infiltration does potentially offer a range of water quality improvements over direct injection to the water table without passage through the unsaturated zone; however, additional treatment options for the non-potable water may still need to be considered, depending on the receiving environment or the end use of the recovered water.     

Dynamics of solutes and dissolved oxygen in shallow urban groundwater below a stormwater infiltration basin

Artificial recharge of urban aquifers with stormwater has been used extensively in urban areas to dispose of stormwater and compensate for reduced groundwater recharge. However, stormwater-derived sediments accumulating in infiltration beds may act as a source of dissolved contaminants for groundwater. Concentrations of hydrocarbons, heavy metals, nutrients and dissolved oxygen (DO) were monitored at multiple depths in shallow groundwater below a stormwater infiltration basin retaining large amounts of contaminated organic sediments. Multilevel wells and multiparameter loggers were used to examine changes in groundwater chemistry occurring over small spatial and temporal scales. Rainfall events produced a plume of low-salinity stormwater in the first 2 m below the groundwater table, thereby generating steep vertical physico-chemical gradients that resorbed during dry weather. Heavy metals and hydrocarbons were below reference concentrations in groundwater and aquifer sediments, indicating that they remained adsorbed onto the bed sediments. However, mineralization of organic sediments was the most probable cause of elevated concentrations of phosphate and DOC in groundwater. DO supply in groundwater was severely limited by bed respiration which increased with temperature. Cold winter stormwater slightly re-oxygenated groundwater, whereas warm summer stormwater lowered DO concentrations in groundwater. Among several results provided by this study, it is recommended for management purposes that infiltration practices should minimize the contact between inflow stormwater and organic sediments retained in infiltration basins.     

Organic micropollutant removal from wastewater effluent-impacted drinking water sources during bank filtration and artificial recharge

Natural treatment systems such as bank filtration (BF) and artificial recharge (via an infiltration basin) are a robust barrier for many organic micropollutants (OMPs) and may represent a low-cost alternative compared to advanced drinking water treatment systems. This study analyzes a comprehensive database of OMPs at BF and artificial recharge (AR) sites located near Lake Tegel in Berlin (Germany). The focus of the study was on the derivation of correlations between the removal efficiencies of OMPs and key factors influencing the performance of BF and AR. At the BF site, shallow monitoring wells located close to the Lake Tegel source exhibited oxic conditions followed by prolonged anoxic conditions in deep monitoring wells and a production well. At the AR site, oxic conditions prevailed from the recharge pond along monitoring wells to the production well. Long residence times of up to 4.5 months at the BF site reduced the temperature variation during soil passage between summer and winter. The temperature variations were greater at the AR site as a consequence of shorter residence times. Deep monitoring wells and the production well located at the BF site were under the influence of ambient groundwater and old bank filtrate (up to several years of age). Thus, it is important to account for mixing with native groundwater and other sources (e.g., old bank filtrate) when estimating the performance of BF with respect to removal of OMPs. Principal component analysis (PCA) was used to investigate correlations between OMP removals and hydrogeochemical conditions with spatial and temporal parameters (e.g., well distance, residence time and depth) from both sites. Principal component-1 (PC1) embodied redox conditions (oxidation-reduction potential and dissolved oxygen), and principal component-2 (PC2) embodied degradation potential (e.g., total organic carbon and dissolved organic carbon) with the calcium carbonate dissolution potential (Ca²⁺ and HCO₃⁻) for the BF site. These two PCs explained a total variance of 55% at the BF site. At the AR site, PCA revealed redox conditions (PC1) and degradation potential with temperature (PC2) as principal components, which explained a total variance of 56%.     

Effects of UV-visible irradiation on natural organic matter from the Amazon basin

The aim of this work was to evaluate the effects of UV-visible irradiation on organic carbon concentration, fluorescence intensity and metal transport ability of the natural organic matter (NOM) at fixed pH values and under several types of atmosphere (air, N(2), O(2)). The water samples were obtained from various sampling sites along the Rio Negro (Amazon basin) and the NOM metal transport ability was determined with regard to Cu(2+). As a first step we measured the concentration of total organic carbon (TOC) and its fluorescence intensity before and after an irradiation for a given time. The results demonstrated that when photodegradation happened, the dominant reactions involved O(2) and the fluorescent sites were among the first to be altered. Then we determined by spectrofluorometry the complexing capacity (C(L)) before and after irradiation. Fluorescence and complexing site densities (C(L)/TOC ratio) increased after a short irradiation time (20 min, i.e. before the photodegradation happened) and decreased after longer irradiation times. Therefore, we conclude that a change of the macromolecular structure activates previously inactive fluorophores and complexing sites prior to photodegradation.     

Comparison of polyaluminum silicate chloride and electrocoagulation process,in natural organic matter removal from surface water in Ghochan,Iran

Removal of natural organic matter (NOM) is one of the most important objectives of water treatment plants but reducing these pollutants either present in water as dissolved or suspended form is not as efficient as is required in conventional treatment plants. The purpose of this study was comparison performance of composite polyaluminum silicate chloride (PASiC) and electrocoagulation (EC) process by aluminum electrodes in NOM removal from raw surface water. In this study, the effects of turbidity, total organic compounds (carbons) (TOC), adsorption at a wavelength of 254 nm (UV254), chemical oxygen demand (COD), alkalinity, residual aluminum in finished water by application of EC process and PASiC were investigated. The results demonstrate that PASiC coagulant at optimum concentration of 1–5 ml/L was capable of removing TOC, COD, U.V., and turbidity from raw water by 93.77, 93.5, 63 and 95 %, respectively. In contrast, EC process, removed TOC, COD, UV and turbidity from raw water by 89, 99.75, 37 and 50%, respectively. The pilot-scale results demonstrated the significant advantage of PASiC compared to EC process in removal of NOM and turbidity form raw water. Residual aluminum in finished water was below the recommended WHO guidelines 0.2 mg/L for both processes. Finally it can be concluded that PASiC and EC process are reliable, efficient and cost-effective methods for removal of NOM from surface water.