J.P. van der Hoek

Quantitative biofouling diagnosis in full scale nanofiltration and reverse osmosis installations.

Biofilm accumulation in nanofiltration and reverse osmosis membrane elements results in a relative increase of normalised pressure drop (DeltaNPD). However, an increase in DeltaNPD is not exclusively linked to biofouling. In order to quantify biofouling, the biomass parameters adenosine triphosphate (ATP), total cell count and heterotrophic plate count in membrane elements were investigated during membrane autopsies and compared with DeltaNPD in test rigs and 15 full scale investigations with different types of feed water. The combination of biomass related parameters ATP and total cell count in membrane elements seem to be suitable parameters for diagnosis of biofouling, whereas plate counts were not appropriate to assess biofouling. The applied DeltaNPD measurement was too insensitive for early detection of fouling. Measurements of biological parameters in the water were shown to be not appropriate in quantifying biofouling. Evidently, there is a need for a practical tool, sensitive pressure drop data and systematic research.

Combined ion exchange/biological denitrification for nitrate removal from ground water under different process conditions

Combined ion exchange/biological denitrification is a process for nitrate removal from ground water in which nitrate is removed by an ion exchanger and the resins are regenerated in a closed circuit through a biological denitrification reactor. On laboratory-scale the process was run under three process conditions. Ground water with a relatively low sulfate concentration (31 mg SO42− 1−1) was treated with the sulfate selective resin Duolite A 165 and with the nitrate selective resin Amberlite IRA 996. In both cases NaCl was used as regenerant. Although the nitrate concentration in the treated water was hardly influenced by the different resin types, chloride and sulfate concentrations were clearly affected. With the nitrate selective resin sulfate concentrations were higher and chloride concentrations were lower as compared with the sulfate selective resin. Treatment of ground water containing a very high sulfate concentration (181 mg SO42− 1−1) was possible by the combined process with the nitrate selective resin. In all three cases sulfate accumulated in the regeneration circuit without imparing the nitrate removal in the service mode. The regenerant was renewed every 2 weeks under one process condition. Compared with conventional ion exchange regeneration this results in a reduction of brine production of 95%.

Sorption and biodegradation of organic micropollutants during river bank filtration: A laboratory column study

This study investigated sorption and biodegradation behaviour of 14 organic micropollutants (OMP) in soil columns representative of the first metre (oxic conditions) of the river bank filtration (RBF) process. Breakthrough curves were modelled to differentiate between OMP sorption and biodegradation. The main objective of this study was to investigate if the OMP biodegradation rate could be related to the physico-chemical properties (charge, hydrophobicity and molecular weight) or functional groups of the OMPs. Although trends were observed between charge or hydrophobicity and the biodegradation rate for charged compounds, a statistically significant linear relationship for the complete OMP mixture could not be obtained using these physico-chemical properties. However, a statistically significant relationship was obtained between biological degradation rates and the OMP functional groups. The presence of ethers and carbonyl groups will increase biodegradability, while the presence of amines, ring structures, aliphatic ethers and sulphur will decrease biodegradability. This predictive model based on functional groups can be used by drinking water companies to make a first estimate whether a newly detected compound will be biodegraded during the first metre of RBF or that additional treatment is required. In addition, the influence of active and inactive biomass (biosorption), sand grains and the water matrix on OMP sorption was found to be negligible under the conditions investigated in this study. Retardation factors for most compounds were close to 1, indicating mobile behaviour of these compounds during soil passage. Adaptation of the biomass towards the dosed OMPs was not observed for a 6 month period, implying that new developed RBF sites might not be able to biodegrade compounds such as atrazine and sulfamethoxazole in the first few months of operation.

RO treatment: selection of a pretreatment scheme based on fouling characteristics and operating conditions based on environmental impact

Amsterdam Water Supply investigated the possibilities of increasing the capacity of the River Dune production plant from 70 to 83 million m3/year. Two possibilities concern the direct treatment of pretreated Rhine River water (C/S/F) by reverse osmosis, without soil passage. In scheme 1, the RO feedwater is pretreated by ozonation, biologically activated carbon filtration and slow sand filtration. In scheme 2 only slow sand filtration is applied as pretreatment of the RO feedwater. To avoid scaling problems with BaSO4 and CaCO3, the RO feedwater was acidified with HCl up to a LSI in the concentrate of 0.0 and the RO units were operated with a recovery of 85%. The use of an anti-scalant (Flocon 100) in combination with H2SO4 dosage (LSI in the concentrate 2.0) and a recovery of 90% was also successful to control scaling, but this operation mode resulted in severe biofouling as the anti-scalant acted as a nutrient for microbial regrowth in the membrane elements. Both pretreatment schemes resulted in an excellent RO feedwater quality with respect to MFI, DOC, AOC and BFR (biofilm formation rate) with an accompanying very stable operation of the RO units. Over a period of 11 months the MTC of the RO units only showed a decrease of 16% and 23% for pretreatment schemes 1 and 2, respectively, while the differential pressure remained constant. Pretreatment scheme 1 is preferred above pretreatment scheme 2 as it results in additional capacity related to disinfection and organic micropollutant removal. Also the RO concentrate is easier to be disposed of from an environmental point of view. Possibilities are mentioned to further optimize scheme 1 with respect to chemical costs and environmental impact.

The use of Biological Activated Carbon Filtration for the Removal of Natural Organic Matter and Organic Micropollutants from Water

Amsterdam Water Supply (AWS) uses Biological Activated Carbon Filtration (BACF) for the removal of natural organic matter in general and the removal of organic micropollutants in particular. In order to minimize costs and environmental burden, it is important to know whether successive reactivations of carbon reduces its effectivity, and whether pesticides are effectively removed after prolonged running times of the carbon filters. The first aspect avoids the necessity of carbon replacement (i.e. costs), while the second aspect reduces the reactivation frequency (i.e. environmental burden). In a future extension scheme, AWS considers the use of an Integrated Mebrane System (IMS), and it is important to know whether the application of BACF is beneficial in the IMS. Six years of operation of BACF in the River-Lake Waterworks (31 million m3/year) have shown that successive reactivations do not affect the DOC removal capacity of the carbon. Three years of operation of BACF in the River-Dune Waterworks (70 million m3/year) have shown that the carbon retains its pesticide removal capacity. The use of BACF in an IMS shows important perspectives in minimizing the fouling of reverse osmosis membranes and in minimizing the organic carbon content in the membrane concentrate.

Retention of herbicides and pesticides in relation to aging of RO membranes

Abstract Amsterdam Water Supply (AWS) intends to increase the capacity of the Leiduin production plant. In the existing plant (capacity 70×10 6 m 3 /y) pretreated Rhine River water was infiltrated in the dune area west of Amsterdam for artificial recharge and after a residence time of approximately 100 days extracted and posttreated to achieve drinking water quality. In the extension (capacity 13×10 6 m 3 /y) the pretreated (coagulation, sedimentation, filtration) Rhine River water was not infiltrated in the dunes, but was treated directly without soil passage. First, an additional pretreatment (ozonation, biological activated carbon filtration and slow sand filtration) was carried out, and finally reverse osmosis (RO) was used for desalination, hardness removal, disinfection and removal of pesticides and others micro-pollutants. Former research on removal of pesticides has already showed a removal of >99.5% with the ozonation/BACF preceding RO. To prove high retention of RO membranes as a second barrier and to examine the influence of aging of the membranes, several dosing experiments were carried out by AWS and Kiwa. During the period before March 1997, Toray SU 710L membranes were used. From then on Fluid Systems 4821 ULP membranes have been used in the RO pilot plant. The RO feed flow is 9 m 3 /h and the recovery is 85%. To compare the removal of pesticides and herbicides with the two different applied RO membranes, six dosing experiments were carried out: two with the Toray membranes and four with the Fluid Systems membranes. A cocktail of pesticides was dosed with a feed concentration of approximately 5 μg/l. The results of the test showed an equal retention for bentazon, DNOC and pirimicarb for both types of membranes. The removal of metamitron and metribuzin was substantially higher with the Fluid Systems membranes. As a result, it was concluded that RO is a second barrier for pesticides in this treatment concept as biological activated carbon filtration in the first barrier. Retention of the Fluid Systems membranes is higher than the retention of the Toray membranes. After 3 years of operation with the Fluid Systems membranes, no pesticide retention decline was observed.

Scaling control of RO membranes and direct treatment of surface water

Abstract Since 1992 Amsterdam Water Supply has been conducting pilot-plant (2 × 9 m3/h) research on the use of reverse osmosis (RO) for direct surface water treatment from the Rhine River. The investigations were made as a feasibility study for an extension with 13 Mm3/y of the existing treatment plant (70 Mm3/y). Research was carried out with ultra-low-pressure membranes and an organophosphonate antiscalant (Permatreat 191). With this antiscalant no biofouling was introduced upon its use. Because of its low environmental impact, sulphuric acid was preferred above hydrochloric acid, but the barium sulfate scaling risk was increased. Experiments were conducted with both types of acid in increasing recovery steps from 80% up to 90%. While starting experimental difficulties with dosing the antiscalant occurred and BaSO4-scale formation was a fact, especially in the installation with sulphuric acid, a severe MTC decrease was seen. Successive cleaning was possible with an alkali cleaner containing a complex builder. From the barium mass balance over this 3-month period, the precipitated barium amount was calculated. Barium analysis of the cleaning solution showed an almost complete recovery of the barium from the membrane elements. Moreover, the MTC was restored completely. From this it was concluded that the precipitated barium sulphate was washed out completely. Recoveries up to 87% are possible without BaSO4-scale formation and run times up to 1 year. The working inhibition time of the antiscalant in concentrate from increasing recoveries was determined experimentally.

Amsterdam as a sustainable European metropolis: integration of water, energy and material flows

ABTRACT Amsterdam has the ambition to develop as a competitive and sustainable European metropolis. The flows of energy, water and resources within the urban environment have a large potential to contribute to this ambition. Through a transition from a linear usage of resources and waste production towards a sustainable management of urban resources with circular flows of resources, the sustainability of cities can be increased. This Urban Harvesting Concept may be applied in Amsterdam. The challenge is how to operationalize this concept in practice. For two municipal companies in Amsterdam, Waternet (responsible for the water management) and AEB (the waste-to-energy company), initiatives were identified on how to do this. The focus is on water, energy, waste and material flows. Circular flows result in economic benefits and sustainability benefits, either expressed as Ecopoints or CO2-emissions. The integration of these flows is especially beneficial.

The effect of redox conditions and adaptation time on organic micropollutant removal during river bank filtration: A laboratory-scale column study

This study investigated the redox dependent removal and adaptive behaviour of a mixture of 15 organic micropollutants (OMPs) in laboratory-scale soil columns fed with river water. Three separate pilot systems were used consisting of: (1) two columns, (2) ten columns and (3) twenty two columns to create oxic, suboxic (partial nitrate removal) and anoxic (complete nitrate removal). The pilot set-up has some unique features--it can simulate fairly long residence times (e.g., 45 days using the 22 column system) and reduced conditions developed naturally within the system. Dimethoate, diuron, and metoprolol showed redox dependent removal behaviour with higher biodegradation rates in the oxic zone compared to the suboxic/anoxic zone. The redox dependent behaviour of these three OMPs could not be explained based on their physico-chemical properties (hydrophobicity, charge and molecular weight) or functional groups present in the molecular structure. OMPs that showed persistent behaviour in the oxic zone (atrazine, carbamazepine, hydrochlorothiazide and simazine) were also not removed under more reduced conditions. Adaptive behaviour was observed for five OMPs: dimethoate, chloridazon, lincomycin, sulfamethoxazole and phenazone. However, the adaptive behaviour could not be explained by the physico-chemical properties (hydrophobicity, charge and molecular weight) investigated in this study and only rough trends were observed with specific functional groups (e.g. ethers, sulphur, primary and secondary amines). Finally, the adaptive behaviour of OMPs was found to be an important factor that should be incorporated in predictive models for OMP removal during river bank filtration.

Climate change mitigation by recovery of energy from the water cycle: a new challenge for water management

Waternet is responsible for drinking water treatment and distribution, wastewater collection and treatment, and surface water management and control (quality and quantity) in and around Amsterdam. Waternet has the ambition to operate climate neutral in 2020. To realise this ambition, measures are required to compensate for the emission of 53,000 ton CO(2)-eq/year. Energy recovery from the water cycle looks very promising. First, calculations reveal that energy recovery from the water cycle in and around Amsterdam may contribute to a total reduction in greenhouse gas emissions up to 148,000 ton CO(2)-eq/year. The challenge for the coming years is to choose combinations of all the possibilities to fulfil the energy demand as much as possible. Only then the use of fossil fuel can be minimized and inevitable greenhouse gas emissions can be compensated, supporting the target to operate climate neutral in 2020.