In order to be able to supply reclaimed water, Spanish regulations (Royal Decree RD 1620/2007) require 90% compliance on a minimum of a 3-month period for quality limits (Table 4.1) that essentially depend on the degree of human exposure. The main parameters chosen for this evaluation are suspended solids and turbidity, as general indicators of the physico-chemical quality of the water and of the likelihood of having an efficient subsequent disinfection, and the concentration ofEscherichia coli, as indicator of the performance of the disinfection process and a measure of the bacteriological quality of the reclaimed water. The determination of parasitic helminth eggs is also required at an unreasonably high frequency and, because they are removed by sedimentation, their presence or absence owes more to the performance of the biological treatment and the clarifiers than to the disinfection process.
Figure 4.1 View of the tertiary treatment at Tossa de Mar and the gravity storage tank for reclaimed water in El Port de la Selva.
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Because of the fact that in Spain the wastewater treatment plant performance is evaluated according to monthly arithmetic averages, but the quality of reclaimed water requires a 90% compliance (90% ile), the operation of water recycling facilities represents a great challenge, requiring not only good qualification and equipment, but also an important mentality change.
Switching from the perspective of compliance of“one out of two”to that of“nine out of ten”is a necessary change to the operators’method that cannot always be guaranteed to happen quickly and smoothly.
All the reclamation treatments are equipped with online probes for the key parameters, so any water suspected of not complying with the standards is not allowed to leave the facility and reach the user.
The probes and online sensors most commonly installed in Costa Brava water reclamation facilities are:
Turbidity: This parameter is continuously measured at the inlet of the reclamation system, so any deterioration in quality of the secondary effluent is detected and can be prevented from entering the system. Since the uses supplied until 2010 were either non-potable urban municipal uses (1.2 in Table 4.1), agricultural irrigation (2.1) or golf course irrigation (4.1), all of which have a limit of 10 NTU, a turbidity sensor was not needed at the outlet of the system, but it may be required in the near future when reclaimed water is delivered for uses such as irrigation of private gardens, for which a limit of 2 NTU has to be observed.
UV output: Any decrease in the intensity of UV light reaching the sensor (i.e. due to lamp aging or burning out, fouling of quartz sleeves, a decrease in water transmittance at 254 nm or a combination of these factors) is detected and recorded. If the intensity falls below a certain level for a certain amount of time, the supply is interrupted as it is no longer possible to guarantee adequate disinfection.
Redox potential: Because in Costa Brava chlorine is always used as a polishing disinfectant agent, after its addition reclaimed water shows an increase in redox potential values, proportional to the chlorine dose. Once calibrated in each of the reclamation plants according to its local conditions and specificities, online monitoring of redox potential is a powerful and reliable tool for the real-time control of disinfection efficiency. If certain values are not achieved, the control loop automatically increases the dose and, if after a certain amount of time those limits are still not met, supply is interrupted, again due to the lack of guaranteed adequate disinfection.
Electrical conductivity: In some reclamation plants where water is used for irrigation, or in the presence of risks for high variations and increase of electrical conductivity, sensors are also used to control the agronomic quality of the product delivered to the end user.
Exceptionally, in the case of the Empuriabrava constructed wetland system, where the use of reclaimed water is mainly intended for environmental purposes, the parameter that is continuously monitored at the outlet of the wastewater treatment plant is the concentration of ammonia, which is a key for a proper performance of the wetland system.
Despite the fact that the concentration ofEscherichia coliis the only parameter required by RD 1620/2007 to measure the efficiency of disinfection, other types of microorganisms are also used to demonstrate the good disinfection efficiency, such as enteroviruses orCryptosporidiumoocysts. As proven by detailed studies conducted in two Costa Brava water reclamation plants (Montemayor et al. 2008), at the usual doses of the installed equipment, the UV light is more efficient than chlorination in terms of inactivation of somatic coliphages and Clostridium spores. The periodic determination of the inactivation values ofClostridiumspores allows an early detection of a loss of performance of the UV system due to lamp aging. Instead, final chlorine addition enables the better control of bacterial regrowth and biofilms in distribution network and provides a chemical tracer for reliability control.
Table 4.1 Summary of the quality criteria for the main categories of water reuse in Spain.
Type of use
Quality criteria (percentile 90%ile)a
SS mg/L Turbidity NTU E. colicfu/100mL Total nitrogen mg N/L
Non-potable urban–residential (1.1) 10 2 0 –
Non-potable urban–municipal (1.2) 20 10 200 –
Irrigation of crops to be eaten raw (2.1) 20 10 100 –
Use in cooling towers and evaporative condensers (3.2)
5 1 0 –
Golf course irrigation (4.1) 20 10 200 –
Aquifer recharge by percolation (5.1) 35 – 1,000 ,10
aAlso, parasitic helminth eggs,1/10 L.
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Table4.2SummaryofthereclaimedwaterqualityofselectedwastewatertreatmentandreclamationfacilitiesinCostaBrava(datafor2010). Typeoffacility
Waterreclamationplant LloretdeMarBlanesLlançàPortdela SelvaEmpuriabravaPalsCastell-Platja d’AroTossadeMar Wastewater treatment (yearof start-up)
Extended aeration(2003)Conventional activated sludge(1974, upgraded 1996) Extended aeration(1995)+ chemical phosphorus removal(2010) Extended aeration (1995) Conventional activated sludge(1983) Conventional activated sludge(1980) Conventional activated sludge(1992, upgraded 2009)
Extended aeration+ chemical phosphorus removal(1998) Reclamation treatment (yearof start-up)
Coagulation, flocculation, multi-media filtration, disinfection (UV+chlorine) (2008) Coagulation, flocculation, multi-media filtration, disinfection (UV+chlorine) (2001) Constructed wetlands(7ha) (1998)
Chlorination (2000)Filtration, disinfection (UV+chlorine) (1998)
“Title-22”d (2003)“Title-22”d (2009)“Title-22”d (2002) Treated volume,m349,80051,9001,202,400410,200798.70060.800386.1002.991.000 Numberof samples59–6957–6115–2730–3652–5849–10550–96123–235 Statistical parametersaAverage90%ileAverage90%ileAverage90%ileAverage90%ileAverage90%ileAverage90%ileAverage90%ileAverage90%ile SS,mg/L2.14.22.64.43.66.22.63.74.47.02.03.25.48.92.54.0 Turbidity,NTU1.22.52.14.02.03.71.31.92.54.11.31.94.06.71.62.5 T254nm,%7564b6956b6456b6760b5750b6958b6155b7267b Totalresidual chlorine,mgCl2/L0.40.2b 1.10.3b –b –c 0.90.4b 2.10.6b 1.20.5b 4.41.3b 0.70.2b E.coli,cfu/100mL22221747190,1,1,14,1,1,1,1,12 Totalnitrogen, mgN/L7.714.214.428.91.11.64.67.429.344.218.930.925.843.17.810.8 Totalphosphorus, mgP/Lc3.36.42.95.61.94.73.86.61.52.93.05.12.44.11.11.8 a Annualarithmeticmeanforalltheparameters,exceptfortheconcentrationofEscherichiacoli,whichisageometricmean.90%ilecorrespondstothepercentile90oftheannualsetofdata. b Resultscorrespondtothepercentile10,hence90%oftheresultsweregreaterthanthevaluedisplayedinthistable. c Notapplicable. d “Title-22”treatmentprocessincludescoagulation,flocculation,clarification,filtrationanddisinfection(UV+Cl2). Integrationofwaterreuse67
Table 4.2 displays a summary of the performance of eight of the treatment facilities in the Costa Brava area in 2010. This selection shows the diversity of technical configurations of both wastewater treatment and reclamation facilities, and thus better illustrates the results of their performance. Selected facilities have been arranged in geographical order, from the one located furthest north (Llançà) to the one located furthest south (Blanes). Except for the extensive Empuriabrava constructed wetland system, all the facilities are technology-intensive, with different types of mechanical equipment. The water reclamation treatment trains are designed for: (1) an improvement in the physico-chemical quality of secondary effluents (reduction of the concentration of suspended solids and turbidity); (2) an adequate inactivation of both pathogenic and indicator microorganisms; and (3) ensuring a chlorine residual in order to preserve the microbiological quality of the water between the production site and the point of use.
Transmittance values at 254 nm are greater in extended aeration plants than in conventional activated sludge plants. This indicates a superior quality of reclaimed water and the likelihood of an easier and more effective disinfection. As it can be deduced from the example of Pals wastewater treatment plant, a good performance of the biological wastewater treatment is critical for producing reclaimed water of the best possible quality. In this case, a well-designed and well-operated biological treatment followed by simple chlorination outperforms all the other reclamation facilities. Nevertheless, an additional tertiary treatment for removal of suspended solids is greatly recommended to ensure the required high disinfection level in the case of variations in the quality of secondary effluents.
As it can be observed in Table 4.2, in which near worst case values are presented (percentile 90 or percentile 10, depending on the kind of parameter), the reclaimed water produced in the Costa Brava facilities has a consistent microbiological quality that complies with Spanish RD 1620/2007 for the intended uses. In the reclamation treatments that perform better, this consistency is also achieved by the other regulatory parameters, such as suspended solids and turbidity.
Generally speaking for the Costa Brava water reclamation facilities, the residual concentrations ofE.coliwere consistently under the detection limit of,1 cfu/100 mL, thanks to the appropriate equipment and continuous monitoring. Similar results were obtained for the other microorganisms such as sulphite-reducingClostridiumspores and somatic coliphages.
The Figure 4.2 illustrates the log inactivation of these indicator microorganisms in the Tossa de Mar reclamation plant. The variations in the monthly average values of inactivation reflect the variations in the concentrations of these microorganisms in secondary effluents. The increasing trend in the inactivation of sulphite-reducingClostridiumspores, the bacterial parameter which is the harder to deactivate, proves that the efficiency and consistency of disinfection has been improved over the years.
The recent addition of somatic coliphages as an indicator of viral inactivation is also important for the protection of the public health, since the inactivation values are always greater than the maximum concentration of enteroviruses found in secondary effluent (2.3 log pfu/L, unpublished data).
0
Somatic colipahes E.coli (Fecal coliforms until 2006) Sulphite-reducing clostridium spores
Figure 4.2 Evolution of the monthly average values of inactivation ofE. coli, sulphite-reducingClostridiumspores and somatic coliphages in the Tossa de Mar reclamation plant (January 2003 to December 2010).
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4.3 WATER REUSE APPLICATIONS
The evolution of water reuse in the Costa Brava has seen three types of projects, which represent the chronological and conceptual evolution that this activity has undergone during the last 20 years:
1 Supply to private large users
Reclaimed water in the Costa Brava started with the supply of reclaimed water (originally disinfected secondary effluents) for the irrigation of golf courses, pitch & put facilities and some agricultural areas, thanks to the favourable regulations and also because the agreements for the supply of rather large volumes to a single or few users, which management is relatively easy.
2 Social or environmental beneficial reuse
Fostered by EU Cohesion Funds since the mid 90’s, Consorci de la Costa Brava and Catalan Water Agency have developed water reuse projects which are beneficial for the sustainable development of the local communities. The two more emblematic projects for environmental enhancement are those of the Empuriabrava constructed wetland system (Figure 4.3), which reclaims water to favour and maintain the biodiversity in a nature reserve, and the Blanes project, in which reclaimed water is used for aquifer recharge in the lower Tordera river.
3 Urban reuse
The most recent water reuse projects happening in some municipalities in the Costa Brava, implemented the installation of reclaimed water distribution pipelines. These pipelines have the long-term intention of delivering water to private users (Figure 4.4, i.e. for the irrigation of home gardens), and represent exactly the opposite situation of the supply to golf courses: small volumes can be supplied to a potentially large number of users and there is no direct connection between the reclamation plant and end-users. Instead, an intermediate operator, usually the municipality, is in charge of recycled water distribution, which often complicates the management of this kind of system.