El Prat de Llobregat Water Reclamation Plant: Reclaimed Water Quality and Reliability

Transcription

1 El Prat de Llobregat Water Reclamation Plant: Reclaimed Water Quality and Reliability P. Aguiló*, J. Sanz**, J. Curto*, B. Martínez* and M. Gullón***. *Empresa Metropolitana de Sanejament EMSSA, Calle Madrazo 50-52, 1º-2ª, 08006, Barcelona, Spain. **VEOLIA Water Solutions & Technologies, Avda Vía Augusta, 3, Edificio Augusta Park, 08174, Sant Cugat del Vallès, Barcelona, Spain. ***Area Metropolitana de Barcelona (AMB), Carrer 62, 16-18, Zona Franca, 08040, Barcelona, Spain. Abstract El Prat Water Reclamation Plant installed in the WWTP of El Prat de Llobregat has been produced reclaimed water since July Up to now, a total of 67.8 hm 3 water from the WRP has been reused. The water reclamation plant has a design flow of 12,600 m 3 /h, and it may reach a maximum treatment flow of 14,400 m 3 /h. This paper present a study about reliability and quality level of reclaimed water produced at the water reclamation plant during the period between July 2007 and December Reliability study with more than 2,500 data points has been made by measuring parameters like turbidity, total suspended solids, BOD 5, COD, total Phosphorus, total Nitrogen and conductivity. Additionally, microbiological quality of reclaimed water produced is emphasized. Sanitary quality parameters analyzed were: Escherichia coli, parasitic helminth eggs, spores of sulphite reducing clostridia, somatic coliphages, Legionella spp, and Legionella pneumophilla. The results obtained confirm that reclaimed water quality produced at water reclamation facility fulfils not only the defined criteria in the current Spanish legislation but also the ones required by the sanitary authority for water reuse. Keywords Reclaimed Water Quality; Reliability; Water Reclamation; Water Reuse INTRODUCTION Since July 2006 El Prat Water Reclamation Plant (WRP) treated secondary effluent from El Prat WWTP producing until the year 2010 a volume of 67.8 hm 3 of reclaimed water, which has allowed increasing the availability of surface water and well water, exclusively for human consumption (Mujeriego et al., 2008). Since start-up, WRP is being operated by EMSSA (Wastewater Metropolitan Company) public company belonging to the metropolitan area of Barcelona, which is an organization formed by 33 municipalities. El Prat WRP is composed by ballasted flocculation treatment followed by surface filtration (Sanz et al., 2007), UV disinfection, and chemical disinfection and produces reclaimed water with chemical and biological quality characteristics required by the Spanish rules for urban, agricultural, industrial, recreation and environmental uses. For more demanding uses like aquifer recharge by water injection, there are an advanced treatment with ultrafiltration and reverse osmosis. The current rules for reclaimed water use, RD1620/2007 (Ministerio de la Presidencia, 2007) establishes control parameters and sampling frequencies, and requires to Health Authorities to prepare an imperative report for each of the uses of reclaimed water. In this report Health Authorities can add new control parameters and sampling frequencies. During these four years of operation, WRP management was carried out two analytical control programs in parallel in order to asset reclaimed water quality and demonstrates capabilities to

2 produce safe reclaimed water by WRP. The internal control program, was carried out by on-site EMSSA laboratory and external control program carried out by independent laboratories, all of them were accredited according to ISO standard. METHODS Unannounced sampling carried out by the external laboratories included grab samples in sterile containers. External laboratory staff is accompanied all times for WRP staff which included a reference sample analyzed by central laboratory of EMSSA. This central laboratory participated in various interlaboratory calibration exercises. This form of sampling guaranteed results accuracy, regardless any action which can be performed at the WRP. Analytical methods of reference for external laboratories are fully agreed and guarantee an exhaustive control of the system, depending on the periodicity of the uses for which reclaimed water is used. Escherichia coli determination is done through the most probable number defined substrate technology. Total suspended solids were analyzed according to EN 872 and the turbidity is determined by Standard Methods 2130B. Nitrogen species was performed according to EN for TKN, while nitrites and nitrates were analyzed by Standard Methods 4500 and 4110 (b), respectively. Total nitrogen was calculated by the sum of the previous parameter. Ammonia was determined by 4500-NH 3 Methods Standard B and C, while phosphorus was analyzed by EN Monitoring of the levels of microbial indicators spores like as sulfite reducing clostridia and somatic coliphages has been done by Microbiology Department of University of Barcelona through an agreement with EMSSA. In the case of the sampling done by EMSSA we differentiate 24h composite samples, mixing individual samples every two hours, which are carried out TSS, Total Nitrogen, Total Phosphorous, and turbidity analytical and a grab sample for E. coli determination. E. coli determination was based on MPN, using the fluorescence emission at 366nm by positive of E. coli that could be present in the water. TSS was determined according to Standard Methods 2540D and the turbidity on Standard Methods 2130B. About analysis methodology for TN and TP exist two periods, the first from June 2007 to May 2008 when TN was calculated from the results of TKN, NO 3, NO 2 (TN = TKN + NO 3 + NO 2 ). Determining TKN used the Standard Methods 4500 Norg-C method and for NO 2 and NO 3 uses the test for rapid detection of Merck RQflex plus. Phosphorus in the first period was determined according to Standard Methods 4500P-B. In the second period (from May 2008 to December 2010) analysis methodology varies and begins to work with kits for rapid detection of Hach Lange, which at the analytical level brings greater sensitivity and at the operational level allows us to optimize the time of analysis. It should be noted that in the second period TN was calculated and becomes a determination which makes the results more reliable and reduces the source of errors associated with the various analytical and subsequent calculation. On the other hand at final year of study the laboratory of EMSSA, according central laboratory methods, in addition to its activity begins to participate in international interlaboratory exercises managed by a company accredited by ENAC according to ISO/IEC 17043: The parameters analyzed were E. coli, TSS, TP, TN, NO 3, and turbidity.

3 RESULTS Percentiles (50th and 90th) of basic parameters controlled have been used to the discussion of the results, using both internal and external control program. The results correspond to the period July December Percentile corresponding to the microbiological parameters has been obtained from accumulated frequencies. Table 1 and 2 shows results from internal and external control program respectively. Table 1. Internal control program (on 24h composite samples excepted microbiological parameters) INFLUENT EFFLUENT Parameter Units N P50 P90 N P50 P90 TSS mg/l BOD 5 mgo2/l <3 <3 COD mgo2/l Turbidity NTU N-NH 4 mg/l N-NO 3 mg/l TN mg/l , TP mg/l Escherichia coli MPN/100mL NA NA NA 513 <1 <1 Fecal coliforms MPN/100mL NA NA NA 451 <1 <1 About E. coli determination it was observed that 98.4% of the samples were below 100 MPN/100 ml (limit fixed by health authorities for water reuse more restricted). On the other hand, more than 90% of the results were below the LOD of the analytical method. In any case was exceeded the limit value fixed by RD1620/2007 as maximum deviation allowed, which is 3.0 ulog/100 ml). Figure 1. Probability distribution of E. coli at reclaimed water according internal control program (N = 513).

4 Table 2. External control program (on specific outlet samples collected by an accredited laboratory without warning in all cases) Parameter Units N P50 P90 TSS mg/l Turbidity NTU N-NH 4 mg/l N-NO 3 mg/l TN mg/l TP mg/l Escherichia coli mg/l 304 <1 <2 Helminth eggs Ova/10L 64 <1 <1 Legionella spp CFU/L 71 <100 <100 Legionella pneumophila CFU/L 50 <100 <100 Again, E. coli determination indicated that 98.4% of the samples were below 100 CFU/100mL, while more than 90% of results were lower than the LOD of the method of analysis. On the other hand, were not observed any positive in nematode eggs during the whole period of study. During these years, had been highlighted also the importance of control and preventive maintenance of UV lamps, main cause sporadic observed malfunction corresponding to E. coli value higher than 100 CFU/100mL. Figure 2. Probability distribution of E. coli at reclaimed water according to external control program (N = 304). Microbial indicator studies applied to water reclamation facilities are a useful tool for ensuring reclaimed water quality (Costán-Longares et al., 2008). The inactivation of some microbial indicators at different points of El Prat WRP treatment was conducted by Microbiology Department of the University of Barcelona (UB) using E. coli, spores of sulphite reducing clostridia, and

5 somatic coliphages. This study analyzed the evolution of these microorganisms at five different points, defined in the following way: Point1: Secondary effluent, point 2: Ballasted flocculation outlet, point 3: Surface filtration (10 micron) outlet, point 4: UV disinfection outlet and point 5: Chemical disinfection by chlorine outlet (reclaimed water) Results obtained are shown in table 3-5. Table 3. Escherichia coli (CFU/100mL) results from UB study. Sampling point N P50 P < <1 3 After UV disinfection, E. coli was lower than 100 CFU/100 ml for 100% of the samples indicating a high degree of disinfection effectiveness. Table 4. Spores of sulphite reducing clostridia (CFU/100mL) results from UB study. Sampling point N P50 P ,500 28, , Table 5. Somatic coliphages (PFU/100mL) results from UB study. Sampling point N P50 P ,500 33, ,200 7, ,900 8, <10 < <10 <10 Figure 3 and 4 evidences that E. coli and somatic coliphages were eliminated mainly by UV disinfection. Figure 5 indicates that spores of sulfite reducing clostridia were removed significantly in ballasted flocculation (more than 1 ulog), and light way in microfiltration. On the other hand, contribution of the chlorination after UV disinfection using 4 mg/l sodium hypochlorite produces no

6 improvement in treatment, fact reflected mainly in the spores of sulfite reducing clostridia removal after the UV disinfection. Figure 3. Probability distribution of E. coli. Figure 4. Probability distribution of somatic coliphages. Figure 5. Probability distribution of spores of sulphite reducing clostridia

7 According RD 1620/2007, reclaimed water quality assessment will take place with the 90 th percentile. For TSS, this value was 5.5 mg/l by internal control and 5.0 mg/l by external control program. Both values were below the minimum value required for all uses which WRP is authorized, because 20 mg/l was the more restrictive requirement. Table 5 shows reclaimed water quality comparative analysis according health protection criteria applied to El Prat WRP. Table 5. Reclaimed water quality comparative analysis according health protection criteria. Parameter Units RD1620/2007 limit Health Authorities limit P 90 Internal control P 90 External laboratory Water reuse TSS mg/l Irrigation and urban Turbidity NTU Irrigation and urban E. coli CFU/100mL < 1 < 2 Irrigation Helminth eggs Ova/10 L 1 1 <1 Irrigation and urban Legionella CFU/ L <100 Urban Environmental reuse correspond to the minimum maintenance of the flow in the Llobregat River and it is the most important fate by quantity of reclaimed water produced (Table 6). Table 6. Reclaimed water quality comparative analysis according health protection criteria. Year Llobregat River and Wetlands Agricultural irrigation Hydraulic barrier against saline intrusion Urban uses ,959, , ,770,742 2,386, ,798 3, ,968, , ,761, ,825,148 0 Total ,460,205 2,386,985 3,117,981 3,681 According water reuse authorization, reclaimed water limits and obtained values for environmental reuse are shown in Table 7. For all parameters required water quality were guaranteed. Table 7. Reclaimed water quality comparative analysis according public health protection criteria. Parameter Units Limit required (percentile) Internal control (percentile) External control (percentile) TSS mg/l 35 (P90) 5.5 (P90) 5 (P90) BOD 5 mgo 2 /L 25 (P90) < 3(P90) COD mgo 2 /L 125 (P80) 44 (P90) P mg/l 2 (P50) 0.7 (P50) 0.69 (P50) TN mg/l 10 (P50) 6.9 (P50) 6.9 (P50)

8 Conclusions El Prat WRP using an internal and external continuous monitoring program demonstrated a reliable operation with a high degree of confidence in the results of quality, while maintaining a 90 th percentile of compliance for all required parameters, according current Spanish legislation and public health authorities requirements for environmental, agricultural irrigation, urban, and industrial water reuse. El Prat WRP reaches a very high level of security from microbiological point of view, because 98% of the samples comply with the rules, and more than 90% of the samples was not detected presence of Escherichia coli (LOD 1 CFU/100mL), which reaffirms it is safe water for water reuse. A rigorous preventive maintenance of the installation, based on surveillance program critical elements of the installation is essential to maintain this level of reliability of the installation: UV lamps, 10 micron filters, etc. When E. coli values were higher than 100CFU/100mL, O&M team detected some UV disinfection malfunctions and repaired and included this return of experience in preventive maintenance practices. Also, microbial indicators study showed that somatic coliphages and spores of sulphite reducing clostridia determination allows to control the functioning of the different steps of the process, allowing highlight problems of operation of the physical-chemical treatment (spores of sulphite reducing clostridia removal), microfiltration and mainly UV disinfection combined with chemical disinfection. References Costan-Longares, A., Montemayor, M., Payán, A., Méndez, J., Jofre, J., Mujeriego, R., and Lucena, F. (2008). Microbial indicators and pathogens: Removal, relationships and predictive capabilities en water reclamation facilities. Water Research, 42, Mujeriego, R., Compte, J., Cazurra, T. and Gullón, M. (2008) The water reclamation and reuse project of El Prat de Llobregat, Barcelona, Spain. Wat. Sci. Tech. 57(4), Ministerio de la Presidencia (2007) Real Decreto 1620/2007, de 7 de diciembre, por el que se establece el regimen jurídico de la reutilización de las aguas depuradas. BOE número 294, de sábado 8 de diciembre de 2007, pp Sanz, J., Ferrer, C., Rodrigo, J.C. and Mujeriego, R. (2007) The Actidisk process for water reclamation: an experimental performance assessment. 6 th IWA Specialist Conference on Wastewater Reclamation and Reuse for Sustainability, Antwerp, Belgium, October 9-12, 2007.