Behaviour of nitrilotriacetic acid during groundwater recharge

A pilot plant study was performed to investigate the behaviour of nitrilotriacetic acid (NTA) during artificial groundwater recharge of river water.The study was designed to investigate the removal of NTA under conditions of artificial groundwater recharge in The Netherlands.The conditions are characterized by relatively low recharge rates and mostly by anaerobic groundwater environments in the aquifers. A further objective of the study was to obtain information on the possible mobilisation of heavy metals from the soil of the aquifer as a result of the formation of NTA-metal complexes.The results suggest that complete removal of NTA during percolation can be expected for concentrations up to 2 mg NTA l⁻¹ in the surface water, even during the period of low water temperatures. The mobilisation of trace elements from the aquifer during the percolation of water containing these low concentrations of NTA was not detected and is considered improbable.     

Removal of asbestos fibres from potable water by coagulation and filtration

There is growing concern that asbestos-like fibres in drinking water could be a potential health hazard. Methods are described for removing asbestiform fibres from potable water based on modifications to conventional water treatment techniques. These include simple sand filtration, diatomaceous earth filtration, chemical coagulation or combinations of these depending on the degree of removal required. The most effective method, involving chemical coagulation with iron salts and polyelectrolytes followed by filtration, resulted in better than 99·8% fibre removal from water containing 12 x 10⁶ fibres 1⁻¹.     

Potable water treatment for some asbestiform minerals: optimization and turbidity data

A study has been undertaken to optimize conventional alum coagulation treatment of water for asbestos fibre removal. The results indicate that both the alum and polyelectrolyte concentrations significantly effect the quality of the treated water. Optimum results were obtained with alum concentrations of 30–50 ppm and polyelectrolyte concentrations of 0.3–0.6 ppm. Rapid coagulation/direct filtration has been evaluated and the results found to be comparable to conventional treatment employing flocculation and sedimentation. A survey of turbidities and fibre concentrations for several municipal water supplies indicate that no systematic relationship exists between these two parameters.     

Chitosan and metal salt coagulant impacts on Cryptosporidium and microsphere removal by filtration

Maintenance of appropriate chemical pretreatment is a critical component of ensuring proper filtration performance. Pilot-scale in-line filtration studies were performed to investigate the relative impacts of chitosan, alum, and FeCl₃ coagulation on the removal of Cryptosporidium parvum oocysts and oocyst-sized polystyrene microspheres by granular media filtration. Similar removals of oocysts and microspheres were achieved when optimal coagulant doses were utilized. Sub-optimal alum and FeCl₃ coagulation resulted in a deterioration filter effluent turbidity (0.2-0.3 NTU) and total particle counts (30-100 total particles ≥2 μm/mL) that were accompanied by reduced (by ∼2-3-log) median oocyst and microsphere removals by filtration. At all doses investigated, chitosan coagulation resulted in excellent turbidity and particle reductions by filtration. Nonetheless, chitosan coagulation at doses of 0.1, 0.5, and 1.0 mg/L did not result in appreciable improvements in C. parvum oocyst removal relative to complete coagulation failure (median oocyst removals were <∼1-log). As well, oocyst-sized polystyrene microspheres appear to be reasonable indicators of C. parvum oocyst removal by in-line filtration preceded by alum and FeCl₃ coagulation, but not chitosan coagulation.     

The Use of Limestone Bed Filtration for the Treatment of Ferruginous Groundwater

A pilot plant, consisting of limestone bed and sand filtration units, has been built 15 km south of Cairo to serve about 400 people. The plant comprises three limestone filter units (operated in series) and two sand filters. Operation of the pilot plant has shown that a packed limestone filter unit is a simple and cheap method of removing iron from ferruginous groundwater. The results demonstrate an iron removal rate of about 60% after passing through one 1.15?m deep limestone filter operating with a surface loading rate up to 1.4 m³/m². h. The overall iron removal after one limestone filter followed by sand filtration was more than 90%.     

Electrodialysis and nanofiltration of surface water for subsequent use as infiltration water

In order to achieve stable groundwater levels, an equilibrium between the use of groundwater for drinking water production and natural or artificial groundwater recharge by infiltration is needed. Local governments usually require that the composition of the water used for artificial recharge is similar to the surface water that is naturally present in the specific recharge area. In this paper, electrodialysis (ED) and nanofiltration were evaluated as possible treatment technologies for surface water from a canal in Flanders, the North of Belgium, in view of infiltration at critical places on heathlands. Both methods were evaluated on the basis of a comparison between the water composition after treatment and the composition of local surface waters. The treatment generally consists of a tuning of pH and the removal of contaminants originating from industrial and agricultural activity, e.g., nitrates and pesticides. Further evaluation of the influence of the composition of the water on the characteristics of the artificial recharge, however, was not envisaged. In a case study of water from the canal Schoten-Dessel, satisfactory concentration reductions of Cl(-), SO(4)(2-), NO(3)(-), HCO(3)(-), Na(+), Mg(2+), K(+) and Ca(2+) were obtained by ultrafiltration pretreatment followed by ED. Nanofiltration with UTC-20, N30F, Desal 51 HL, UTC-60 and Desal 5 DL membranes resulted in an insufficient removal level, especially for the monovalent ions.     

Sensory properties and analysis of two muddy odour compounds, geosmin and 2-methylisoborneol, in water and fish

Muddy or earthy odours are a problem in water supplies and fisheries. Some species of aquatic actinomycetes and blue-green algae are generally indicated as sources of muddy odour in natural waters. These organisms are capable of producing the muddy-smelling compounds geosmin and 2-methylisoborneol.The sensory properties of geosmin and 2-methylisoborneol in water and in the flesh of four species of fish were studied. Threshold odour concentrations are presented, and they indicate that both compounds have strong odour characteristics. The intensity of the muddy odour as perceived by the judges was proportional to the logarithm of the concentration of muddy odour compounds in the concentration ranges tested (for geosmin, up to 100 μgkg⁻¹, and for 2-methylisoborneol, up to 10 μg kg⁻¹). The results indicate that it may be possible to quantify muddy odour compounds in water and fish by sensory methods.     

Removal of biodegradable dissolved organic carbon in a water treatment plant

A new scheme of treatment has been developed in the water treatment plant of Ivry-sur-Seine near Paris. This treatment consists of a pretreatment of preozonization, contact coagulation, coagulation on a filter, slow sand filtration, ozonization and GAC filtration. We have tested the efficiency of this new line of treatment for the removal of BDOC and have attempted to correlate the results with the removal of organic matter (global parameters). Results show a very good efficiency of slow sand filtration and we think that this treatment step allows production of a biologically stable water.     

Effect of temperature on algal removal from wastewater stabilization ponds by alum coagulation

Questions about the effect of temperature on algal cell coagulation and the relationships between algae removal and temperature, alum dosage, paddle speed, flocculation time, and settling time are answered. The investigations consisted studies on algae in wastewater stabilization ponds. The jar-test technique was used for the coagulation of algal suspension by alum.Analysis of variance of the variables and their interactions showed significantly the effect of all variables and most of their interactions. Step-wise multiple regression technique was used for the development of mathematical models for the estimation of algal removal.Increased temperatures adversely affected the percentage removal of algal cells by alum coagulation. Alum was effective in removing algae from Logan wastewater stabilization ponds. However, high alum dosage are required which may not be justified economically.     

Occurrence and removal of pharmaceuticals and hormones through drinking water treatment

The occurrence of fifty-five pharmaceuticals, hormones and metabolites in raw waters used for drinking water production and their removal through a drinking water treatment were studied. Thirty-five out of fifty-five drugs were detected in the raw water at the facility intake with concentrations up to 1200 ng/L. The behavior of the compounds was studied at each step: prechlorination, coagulation, sand filtration, ozonation, granular activated carbon filtration and post-chlorination; showing that the complete treatment accounted for the complete removal of all the compounds detected in raw waters except for five of them. Phenytoin, atenolol and hydrochlorothiazide were the three pharmaceuticals most frequently found in finished waters at concentrations about 10 ng/L. Sotalol and carbamazepine epoxide were found in less than a half of the samples at lower concentrations, above 2 ng/L. However despite their persistence, the removals of these five pharmaceuticals were higher than 95%.     

Colour and turbidity removal with reusable magnetite particles—VI: Pilot plant operation

A novel process which utilizes fine magnetite particles for the removal of colour and turbidity from water has been tested in a 60 1 min⁻¹ pilot plant on water from an unconfined aquifer in Perth, Western Australia. The performance of the pilot plant closely matched jar test results. The process design was optimized to achieve a high quality product water on a raw feed which was difficult to treat in the conventional alum coagulation and filtration plant. A comparison of the conventional and magnetite treatment systems is made, which shows that the magnetite process is viable as an alternative water treatment technique.     

Occurrence and fate of the antidiabetic drug metformin and its metabolite guanylurea in the environment and during drinking water treatment

Metformin, an antidiabetic drug with one of the highest consumption rates of all pharmaceuticals worldwide, is biologically degraded to guanylurea in wastewater treatment plants. Due to high metformin influent concentrations of up to 100 μg/L and its high but incomplete degradation both compounds are released in considerable amounts of up to several tens of μg/L into recipient rivers. This is the first systematic study on their environmental fate and the effectiveness of treatment techniques applied in waterworks to remove metformin and guanylurea from surface water influenced raw waters. The concentrations in surface waters depend strongly on the respective wastewater burden of rivers and creeks and are typically in the range of about 1 μg/L for metformin and several μg/L for guanylurea but can reach elevated average concentrations of more than 3 and 20 μg/L, respectively. Treatment techniques applied in waterworks were investigated by an extended monitoring program in three facilities and accompanied by laboratory-scale batch tests. Flocculation and activated carbon filtration proved to be ineffective for removal of metformin and guanylurea. During ozonation and chlorination experiments with waterworks-relevant ozone and chlorine doses they were partly transformed to yet unknown compounds. The effectiveness of the treatment steps under investigation can be ordered chlorination > ozonation > activated carbon filtration > flocculation. However, most effective for removal of both compounds at the three full-scale waterworks studied proved to be an underground passage (riverbank filtration or artificial groundwater recharge). A biological degradation is most likely as sorption can be neglected. This is based on laboratory batch tests conducted with three different soil materials according to OECD guideline 106. Since such treatment steps were implemented in all three drinking water treatment plants, even traces of metformin and its metabolite guanylurea could not be detected at the end of the treatment trains. Both can only be expected in finished drinking water if surface influenced raw water is used by direct abstraction without underground passage.     

Enhanced coagulation for high alkalinity and micro-polluted water: the third way through coagulant optimization

Conventional coagulation is not an effective treatment option to remove natural organic matter (NOM) in water with high alkalinity/pH. For this type of water, enhanced coagulation is currently proposed as one of the available treatment options and is implemented by acidifying the raw water and applying increased doses of hydrolyzing coagulants. Both of these methods have some disadvantages such as increasing the corrosive tendency of water and increasing cost of treatment. In this paper, an improved version of enhanced coagulation through coagulant optimization to treat this kind of water is demonstrated. A novel coagulant, a composite polyaluminum chloride (HPAC), was developed with both the advantages of polyaluminum chloride (PACl) and the additive coagulant aids: PACl contains significant amounts of highly charged and stable polynuclear aluminum hydrolysis products, which is less affected by the pH of the raw water than traditional coagulants (alum and ferric salts); the additives can enhance both the charge neutralization and bridging abilities of PACl. HPAC exhibited 30% more efficiency than alum and ferric salts in dissolved organic carbon (DOC) removal and was very effective in turbidity removal. This result was confirmed by pilot-scale testing, where particles and organic matter were removed synergistically with HPAC as coagulant by sequential water treatment steps including pre-ozonation, coagulation, flotation and sand filtration.     

Biological clogging of sand and changes of organic constituents during artificial recharge

Biological clogging during artificial ground water recharge is divided into three stages, i.e. aerobic period, transitional period from aerobic conditions to anaerobic conditions and anaerobic period. During the transitional period, the infiltration rate is almost constant or increases slightly because of the transient decrease of microbial accumulation in the sand column. Experimental result shows that the secondary effluent infiltrated through the sand must have SS (Suspended Solids) of < 2 mg 1⁻¹ and SOC (Soluble Organic Carbon) of < 10 mg 1⁻¹ to maintain a high infiltration rate during a long inundation period. The gel chromatogram data show that the biological clogging plays an important role in preventing contamination of an aquifer during recharge by polluted water.     

Degradation of DBPs' precursors in river water before and after slow sand filtration by photo-Fenton process at pH 5 in a solar CPC reactor

The generation of disinfection by-products during water treatment can be controlled by reducing the levels of precursor species prior to the chlorination step. The Natural Organic Matter (NOM) is the principal organic precursor and conventional removal of pollutants such as coagulation, flocculation and filtration do not guarantee the total NOM removal. In this study the degradation of NOM model compounds (dihydroxy-benzene) as well as the removal of NOM from river water via photo-Fenton process in a CPC solar photo-reactor is presented. The effect of solar activated photo-Fenton reagent at pH 5.0 before and after a slow sand filtration (SSF) in waters containing natural iron species is investigated and the details reported. The results showed that the total transformation of dihydroxy-benzene compounds along a mineralization higher than 80% was obtained. The mineralization of the organic compounds dissolved in natural water was higher than in Milli-Q water, suggesting that the aqueous organic and inorganic components (metals, humic acids and photoactive species) positively affect the photocatalytic process. When 1.0 mg/L of Fe³⁺ is added to the system, the photo-Fenton degradation was improved. Therefore the photo-Fenton reagent could be an interesting complement to other processes for NOM removal. Comparing the response of two rivers as media for the organic compounds degradation it was observed that the NOM photo-degradation rate depends of the water composition.     

Quality aspects of ozonisation

Only at relatively low initial values of colour, taste and organic compound content, ozonisation can lead to a quality of drinking water that meets the requirements. In combination with other processes ozone can give a considerable reduction when removing colour and taste from strongly polluted surface water (60 and 75% respectively). One often needs artificial recharge or coagulation before applying ozonisation and carbon filtration after ozonisation. The organic compound content is reduced by ozone to only a small extent (10% of the TOC). In many of the cases investigated a dosage of more than 2 to 2.5 mg 1⁻¹ ozone seems to bring about no further effect. Yet, for the colour reduction of ground water from the isle of Ameland there appeared to be indications of a dosage of 5 mg 1⁻¹ ozone being optimal. The optimal dosage for other types of water is still to be investigated.     

砂滤床直接过滤机理的研究

以含有高岭土人工配制水的混凝和直接过滤实验研究为基础，探讨了砂直接过滤去除水中悬浮微粒的机量以及烧杯混凝实验最佳投药量与直接过滤最佳投药量的关系。     

Removal of bulk dissolved organic carbon (DOC) and trace organic compounds by bank filtration and artificial recharge

Bank filtration and artificial recharge provide an important drinking water source to the city of Berlin. Due to the practice of water recycling through a semi-closed urban water cycle, the introduction of effluent organic matter (EfOM) and persistent trace organic pollutants in the drinking water is of potential concern. In the work reported herein, the research objectives are to study the removal of bulk and trace organics at bank filtration and artificial recharge sites and to assess important factors of influence for the Berlin area. The monthly analytical program is comprised of dissolved organic carbon (DOC), UV absorbance (UVA254), liquid chromatography with organic carbon detection (LC-OCD), differentiated adsorbable organic halogens (AOX) and single organic compound analysis of a few model compounds. More than 1 year of monitoring was conducted on observation wells located along the flowpaths of the infiltrating water at two field sites that have different characteristics regarding redox conditions, travel time, and travel distance. Two transects are highlighted: one associated with a bank filtration site dominated by anoxic/anaerobic conditions with a travel time of up to 4-5 months, and another with an artificial recharge site dominated by aerobic conditions with a travel time of up to 50 days. It was found that redox conditions and travel time significantly influence the DOC degradation kinetics and the efficiency of AOX and trace compound removal.     

Estimation of norovirus removal performance in a coagulation-rapid sand filtration process by using recombinant norovirus VLPs

Norovirus (NV) is an important human pathogen that causes epidemic acute nonbacterial gastroenteritis worldwide. Because of the lack of a cell culture system or an animal model for this virus, studies of drinking water treatment such as separation and disinfection processes are still hampered. We successfully estimated NV removal performance during a coagulation-rapid sand filtration process by using recombinant NV virus-like particles (rNV-VLPs) morphologically and antigenically similar to native NV. The behaviors of two widely accepted surrogates for pathogenic waterborne viruses, bacteriophages Qβ and MS2, were also investigated for comparison with that of rNV-VLPs. Approximately 3-log₁₀ removals were observed for rNV-VLPs with a dose of 40 μM-Al or -Fe, as polyaluminum chloride at pH 6.8 or ferric chloride at pH 5.8, respectively. Smaller removal ratios were obtained with alum and ferric chloride at pH 6.8. The removal performance for MS2 was somewhat larger than that for rNV-VLPs, meaning that MS2 is not recommended as an appropriate surrogate for native NV. By comparison, the removal performance for Qβ was similar to, or smaller than, that for rNV-VLPs. However, the removal performances for rNV-VLPs and Qβ differed between the coagulation process and the following rapid sand filtration process. Therefore, Qβ also is not recommended as an appropriate surrogate for native NV.     

Nitrogen transformation in wastewater reclamation

Nitrogen transformation was examined in the sequential stages of wastewater treatment in the Dan Region Wastewater Reclamation Project in Israel. It was shown that volatilization, assimilation and nitrification were the mechanisms responsible for ammonia removal from the water during various treatment stages. When the recharge basin dried, nitrification occurred, leading to removal of ammonia and accumulation of nitrate in the sand. Upon flooding the recharge basin nitrate was leached from the sand and accumulated in the groundwater, while ammonia was adsorbed to particles in the sand layers.