Water Quality of Drinking Water Resources and Formation of Disinfection by-products

Transcription

1 Egyptian-German Workshop on Sustainable Water Technologies (SusWaTec Workshop) th February Cairo, Egypt Water Quality of Drinking Water Resources and Formation of Disinfection by-products Prof Dr. Mohamed I. Badawy National Research Centre, Water Pollution Research Department Dokki, Cairo, Egypt badawy46@hotmail.com 1

2 Contents Challenges in water Quality. Disinfection By-Products (DBPs) in Four Drinking Water Treatment Plant in Greater Cairo. Minimization of the formation of DBPs. 2

3 Objectives Evaluation of River Nile water quality. Impacts of the water quality. The formation of Disinfection byproducts. Emphasis on chlorine DBPs. Minimization of the formation of disinfection by-products

4 Water Supply The River Nile forms the main water resource of Egypt. According to Sudan agreement a stable 55.5 billion m 3 /yr. was allocated to Egypt, which represents 95 % of all renewable water resources. Ground Water: Four different groundwater aquifers: the Nile Aquifer, the Nubian Sandstone Aquifer, the Moghra Aquifer and the Coastal Aquifer. Each resource has its limitations on use. These limitations relate to quantity, quality, location, time, and cost of development. The maximum renewable amount of ground water is around 7.5 BCM. Average rainfall in Egypt is estimated at 18 mm or 1.8 billion m³ per year. Furthermore. Non-conventional water resources include agricultural drainage water, desalinization of brackish groundwater and/or seawater, and treated municipal wastewater. The total amount of such indirect reuse is estimated to be about 12,6 BCM/year. 4 SusWaTec Workshop 19 February 2013

5 Water Demand Various demands for freshwater are exerting excessive pressure on the available water supply. The agricultural sector (including fisheries) is the highest freshwater consumer, utilizing about 86% of the available supplies. The domestic and industrial sectors consume 7% and 8% of the total natural supplies. It is now evident that nonconventional water sources of freshwater are necessary to meet the current and future freshwater demand. 5 SusWaTec Workshop 19 February 2013

6 Population growth and per capita water share in Egypt (m 3 /year) It is worth mentioning that the availability of renewable water resources in Egypt has dropped from 1500 m 3 /capita/year in 1966 to 700 m3/capita/year in Today, the per capita water availability of less than 700 m3 per year in Egypt is already below the water poverty line of 1,000 m3 per capita a year, accepted by the World Bank Furthermore, it is forecasted that in 2025 the population will reach 95 million, which would mean a per capita share of only 600 m³ per year 6 SusWaTec Workshop 19 February 2013

7 2- Source of Water Pollution 7

8 2.1. Wastewater discharges Nile River from Aswan to Delta Barrage receives wastewater discharge from 124 point sources, of which 67 are agricultural drains and the remainder is industrial and domestic sources. 8

9 2.2 -Industrial Waste Water Egyptian industry uses 7.6 Bm 3 /yr of water. The River Nile supplies 65% of the industrial water needs and receives more than 57% of its effluents. 12 % treat their wastes a complete scientific treatment, 14 % partially treat their wastes and the 74 % don't treat them at all. Food industries contribute to 45% of total effluent discharge and to 67% of the total BOD load introduced. However, the chemical industry is responsible for more than 60% of the heavy metal discharges 9

10 2.3-Agricultural drainage water The agricultural drainage of the southern part of Egypt returns directly to the Nile River where it is mixed with the Nile fresh water. The total amount of such indirect reuse is estimated to be about 4.07 BCM/year. In the Delta region the amount of agricultural drainage water reuse officially was estimated to be around 4.27 BCM/year, in addition to about 0.3 BCM/year lifted to surface water (Rossetta branch) from west delta drains. Additional unofficial reuse done by farmers themselves has been estimated to be around 2.8 BCM/year. The remaining drainage water is discharged to the sea and the northern lakes via drainage pump stations. The total amount of drainage water that was pumped to the sea has been estimated to be BCM/year. 10

11 2.4-Domestic Wastewater The amount of collected wastewater is about 6.5 BCM /Yr 3.65 BCM /Yr (Treated) 2.85 BCM /Yr (not Treated) (5 % of Nile Share) 20 % Primary (0.73BCM) 80% Secondry (2.92 BCM) 11

12 Activated Sludge Treatment Plant 12

13 Other biological treatment techniques Oxidation Pond Aerated Lagoons 13

14 3- Impact of Wastewater Discharge The constituents of concern in domestic and municipal wastewater are pathogens, parasites, nutrients, oxygen demanding compounds and suspended solids. High levels of toxic substances in industrial wastewater have been reported such as heavy metals & organic micro-pollutants. Trace micro-pollutants are mainly attached to suspended material, most of it accumulates in the sludge. Improper sludge disposal and/or reuse may lead to contamination of surface and ground water. 14

15 3- Impact of Wastewater Discharge (Cont.) Increased salinity due to agricultural drainage reuse. Drainage return flow to the Nile result into an increase in salinity of the water from 130 mg/l at Aswan (far upstream) to 250 mg/l near the delta barrage. Organic and inorganic pollution associated with disposal of untreated or partially treated industrial effluents into water ways (mainly drains) at specific locations and hot spots. Pollution resulting from agrochemicals and pesticides. 15

16 3- Impact of Wastewater Discharge (Cont.) Formation of chlorine DBPs in treated water Chlorination is one of the most widely used disinfection processes in water treatment plants in Egypt to ensure a safe drinking water. The Nile River supplies about 97 % of the annual renewable drinking water resources in Egypt. One of the major quality problems facing the use of surface water for drinking purposes is the formation of carcinogenic compounds such as DBPs due to the reaction of NOM with chlorine during drinking water treatment processes. Numerous treated water samples collected from various locations in Egypt have shown high THM and HAA levels. 16

17 4- DBPs Precursors and DBPs Levels in DWTPs in Greater Cairo A Case Study 17

18 Introduction This study is a joint research project between NRC, Egypt and University of South Carolina, USA, aims to: Develop an efficient treatment scheme for drinking water containing NOM and reduction of formation of DBPs (THMs and HAAs). To achieve this task different treatment schemes were investigated consisting of enhanced coagulation, sedimentation, disinfection by using chlorine dioxide, ozone, filtration by sand filter, and/or GAC. 18

19 Introduction (Cont.) Disinfection of water during treatment process Intake Screening Prechlortination Raw water should have low concentrations of all contaminants. Sedimentation Flocculation Coagulation Exhibit minimal variability from day to day. Sand filtration Postchlorinatin Distribution Disinfection of water during distribution By avoiding the contamination of water resource, water treatment becomes easier, less expensive and more quality. 19 SusWaTec Workshop 19 February 2013

20 Introduction (Cont.) NOM DBPs Several studies reported that these compounds have been related to: Cl 2 occurrence of cancer, growth retardation, spontaneous abortion, and congenital cardiac defects THMs CHCl 3 CHCl 2 Br CHClBr 2 CHBr 3 HAAs MCAA DCAA TCAA MBAA DBAA Factors affecting DBPs formation: ph, temperature, dissolved organic carbon (DOC), bromide concentrations, and operational factors (chlorine dose, contact time). 20 SusWaTec Workshop 19 February 2013

21 Experimental Monitoring program was conducted in 4 drinking water treatment plants which are located in Giza and Cairo Governorates. El-Dahab Island and Embaba DWTPs were selected in Giza Governorate. In Cairo Governorate, Mostorod and Fostat DWTPs were chosen. Several samples were collected from each treatment step including inlet, after clarifier, after sedimentation, and finally from plant outlet 21 SusWaTec Workshop 19 February 2013

22 Parameters related to DBPs formations Physico chemical parameters related to DBPS formation such as Turbidity, ph, residual CL2, conductivity,.(גּ 455 Alkalinity and Color(at TOC& DOC which give an indication on the natural organic matter (NOM). UV 254 and specific Ultraviolet absorption at 254 nm (SUVA 254 ), an indicator of carbon aromaticity in water and hydophlocity of NOM. Parameter TOC DOC Algae UV 254 SUVA 254 THMs HAAs Sample Intake Clarifi er Filter Outlet Location s Cairo Mostorod DWTP Fostat DWTP Giza El-Dahab Island DWTP Embaba DWTP. 22

23 Results Average NOM contents in raw waters were 5.14, 4.43, 4.24 and 3.28 mgc/l with an average UVA 254 of 0.1, , , and L/mg-M at Embaba, El-Dahab Island, Fostat and Mostorod DWTPs, respectively. In parallel, SUVA 254 values in all DWTPs were also in the low to medium range ( L/mg-M) This indicates that NOM in raw waters is of low molecular weight with hydrophobic and aromatic characteristics. 23

24 Seasonal variation of raw water quality Parameters Unit Range Average PH Turbidity NTU Color mg/l Pt- Co Conductivity µs/cm Alkalinity mg/l CaCO DOC Mg /L TOC mg/l UV 254 1/cm SUVA 254 1/mg*m

25 Seasonal Variations of surrogate Parameters ph did not display seasonal variation and remains constant around 7.5. Both turbidity and UV absorbance showed strong seasonal variation since The turbidity values increased in summer52 NTU and 6.5NTU in spring season respectively DOC TOC SUV UV 10 While in winter and autumn there were no significant change in its value. 2 1 TOC increased moderately in spring season to reach 5.11mgC/l. Maximum true color (455 nm) was observed in winter season (41 Pt/Co). 0 Jan Feb March April May June July Augst Sept Oct Nov Dec 25

26 Removal Percent % DWTP Performance efficiency The obtained results indicated that the DWTS are not very effective in removal of total organic carbon (TOC), especially DOC removal was about 9 %. The conductivity of the water samples slightly increased through the treatment stages. PH of the collected samples was nearly constant within the treatment steps ,9 89,7 20, Alkalinity of the collected samples was decreased through the treatment steps by 20.47%. 0 26

27 Results To assess the Efficiency of DWTPs, samples were collected from the treatment stages. The parameters related to DBPs formations were analyzed in each sample. Current treatment processes were found to be effective in the removal of suspended solids as turbidity values reduced by 90.06%, 87.25%, 90.73% and 87.86% in Embaba, El-Dahab Island, Fostat and Mostorod DWTPs, respectively. The conductivity removals were 25.91, 15.90, 1.79 and 8.25% for Embaba, El-Dahab Island, Fostat and Mostorod DWTPs, respectively. In general, the studied DWTPs were relatively not very effective in removal of total organic carbon (TOC) since the removal percentages of DOC in Embaba, El-Dahab Island, Fostat and Mostorod DWTPs were 32.41, 22.35, 22.64, 14.63%, respectively. The DOC removal might be due to reaction between chlorine used in disinfection and DOC and/or adsorption on sand filter. The low DOC percent removal indicates that water after passing through settling basins and filters was still loaded with organic matter. Consequently, the latter compounds would contribute to increase the levels of THMs as the retention time is extended during the water treatment processes. 27

28 % Removal of algae in the studied DWTPs Percentage of algal removal ranged between 77.7 to 84.8% of the total algae count of raw water samples as an average value between 4 different water treatment plants. After sand filtration composition of algae was further changed. and diatoms represent the highest ratio in the outlet water. It is indicated the abilities of diatoms algae to pass through the sand filter due to their spindle structure and their small size After Clarifier After Filtration Final Outlet Final Outlet After Filtration After Clarifier 28

29 Efficiency of DWTPs in Bacteria Removal The studied DWTPs showed high efficiency for the removal of bacteria from raw water. The reduction in total bacterial count mostly occurs after prechlorination process (70-88%). The remaining counts removed after postchlorination at the DWTPs outlets. Total Coliform, Fecal Coliform and Fecal Streptococci were absent in all samples after clarification. 29 SusWaTec Workshop 19 February 2013

30 Determination of Optimal Treatment Processes for Natural Organic Matter Removal and Disinfection By- Product Formation Reduction Mohamed I. Badawy a, Tarek A. Gad-Allah a,, Mohamed E.M. Ali a, Yeoman Yoon a Water Pollution Research Department, National Research Centre, P.O. Box 12311, Dokki, Cairo, Egypt b Department of Civil/Environmental Engineering, University of South Carolina, Columbia, SC 29201, USA 30

31 Factors Affecting DBP Formation Water quality - TOC - Temperature - ph - Bromide Disinfectant used - Chlorine - Chloramine - Chlorine dioxide - Alkalinity - Turbidity - Other components - Ozone Point of disinfection Time

32 Effect of TOC and UV254 NOM + Cl2 THMs + HAAs + other DBPs. TOC is one of the most widely used measures for quantifying the amount of NOM in water. DOC represented the relative amount of precursor material UV254 has been widely used to predict (DOC) in water or its reactivity in forming disinfection by-products. The results show that a higher available TOC or UV254 will provide more DBPs.

33 SUVAs and DBPS formation The SUVA reflects the hydrophobic fraction of organic matter. Waters with a low humic acid fraction have SUVAs less than 3 L/mg m, while waters with a high humic acid fraction have SUVAs between 3 and 5 L/mg m. The obtained results showed the SUVA is less than 3 L/mgm, therefore the effect of the coagulant dosage may be negligible and relatively low removal percentages and high levels of DBPs formation were obtained.

34 HAAs (µg/l) Concentrtion (µg/l) Effect of Contact Time Cl 2 reacts very fast to produce reasonable amounts of THMs and HAAs within short time (30 min); the subsequent increase is slightly slow. (a) CHCl3 CHClBr2 CHCl2Br CHBr3 The increase in THMs and HAAs concentration with time is due to more contact between Cl 2 and NOM present in water It is interesting to note that the extent of formation varies from one compound to another. THMs CHCl 3 : (i.e., 76%) within 100 min. CHBr 2 Cl: 14% within 100 min CHBr 3 : 20% within 100 min CHBrCl 2 : the most affected, 55% increase in 100 min. HAAs MCAA: µg/l i.e % within 90 min DCAA and TCAA: 26, and 25 %, respectively in the same time intervals. Brominated acetic acid compounds were not detected. (b) Time (min) MCAA DCAA TCAA Time (min) 34

35 HAAs (µg/l) Concentrtion (µg/l) Effect of ph increasing ph from 5 to 8.5 has significant effect on the formation of DBPs (a) CHCl3 CHCl2Br CHClBr2 CHBr3 600 Maximum yields of THMs ph Maximum yields of HAAs ph 8. (b) ph (-) MCAA DCAA TCAA 1200 At high ph values: decomposition of many halogenated DBPs occurs and the concentration of DBPs decreased ph (-) 35

36 Concentrtion (µg/l) Concentrtion (µg/l) Effect of initial Cl 2 dose In general, as chlorine dose is increased, THMs and HAAs yield attains higher values. However, THMs formation was not directly proportional to the applied chlorine dose. The DOC in real surface waters is a contribution of different organic compounds and some substances are not THM precursors. and/or that chlorination yields several halogenated organics other than THMs. Among the four THMs, CHCl 3 was the dominant species and occupied over 69 % of the total THMs concentration (TTHM). (a) CHCl3 CHCl2Br CHClBr2 CHBr3 (b) MCAA DCAA TCAA Initial Cl 2 dose (mg/l) Effect of Chlorine dose on (a) THMs and (b) HAAs formation Initial Cl2 dose (mg/l) 36

37 Effect of bromide ion In the formation of THMs, with the Br content increasing, the content of DCBM, DBCM and TBM increase. In general, TBM concentration increases slightly with increasing bromide ion concentration. But, a slight decrease in TTHM with higher Br dosage. The results show that in the compositions of DBPs, with the increasing Br concentration, the component of chlorine decreased gradually, and the component of bromine increased. 37

38 Concentrtion (µg/l) HAAs (µg/l) Effect of initial TOC concentration THMs Chloroform is the most affected compound Other compounds were slightly affected by TOC value. HAAs MCAA concentration increased by 20 %. DCAA and TCAA concentration increased by 49 and 40 %, respectively. TOC : 10 mg/l 15 mg/l (a) 1600 CHCl3 CHCl2Br CHClBr2 CHBr3 (b) 1400 MCAA DCAA TCAA TOC (mgc/l) TOC (mgc/l) Effect of initial TOC concentration on (a) THMs and (b) HAAs formation 38

39 Concentration (ug/l) Concentration (ug/l) DOC fractions and their contribution in DBPs formation For understanding of the correlation between DOC fractions and DBPs formation, a series of bench scale experiments were conducted. Raw water sample was collected from Nile River and then fractionated. Finally, each fraction was chlorinated with 5 mg/l Cl 2 for one hour. the DBPs formation for the hydrophilic species was usually higher than that of hydrophobic species. This indicated that the hydrophilic fraction was a more reactive precursor for THMs than the hydrophobic fraction. CHCl3 CHCl2Br CHClBr2 CHBr Raw HPL HPO TPL MCAA DCAA TCAA MBAA BCAA DBAA Raw HPL HPO TPL Contribution of DOC fractions in DBPs formations, (a) THMs and (b) HAAs 39

40 Disinfection by-products (DBP) levels 40

41 % THMs Removal (DBP)formation The concentration found to increase through the processes about 27% of THMs formed in flash mix process (the point of chlorine addition). While 43% of THMs occurs in slow mix unit and reach to 72% of their value through sedimentation and 75% through filtration. After the post chlorine is added THMs increased with about 25%

42 Disinfection by-products (DBP) levels after the storage tank THMs and HAAs are the most important groups of DBPs. The average concentrations of TTHMs were 64.38, 43.94, and µg/l in water samples collected from the outlet of Embaba, El-Dahab Island, Fostat and Mostorod DWTPs, respectively, which still less than the Egyptian standards for Drinking Water Quality (100 µg/l). While the corresponding average concentrations of HAAs were 57.64, 54.79, and µg/l for Embaba, El-Dahab Island, Fostat and Mostorod DWTPs, respectively. The average concentration of studied HAAs was on the margin of the maximum contaminant level of 60 μg/l 42

43 TTHMs for Summer Event in Nasr City Tap Water Smith and El Deen (2009) 43

44 Concentration (µg/l) The monthly change of THMs A relative decrease in concentration of THMs was noticed during January to March. The levels of THMs increased started from March until May. CHCl3 CHCl2Br CHClBr2 CHBr3 TTHM (a) TOC increased moderately in the same period to reach 5.2mgC/l Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. 44 SusWaTec Workshop 19 February 2013

45 Minimization of the formation of disinfection by-products Mohamedy. Badawy a, Tarek A. Gad-Allah a,,mohamed.m. Ali a, Yeoman Yoon b a Water Pollution Research Department, National Research Centre, P.O. Box 12311, Dokki, Cairo, Egypt b Department of Civil/Environmental Engineering, University of South Carolina, Columbia, SC 29201, USA 45

46 OVERVIEW Atmosphere Off-Gas Ozone Destruction Influent Effluent Ozone Quench (Option) Ozone Gas Gas Feed System Ozone Generator 46

47 Technologies for the reduction of DBP formation Enhanced coagulation Granular activated carbon Membrane filtration Alternate disinfectants Chlorine dioxide Ozone 47

48 Additional Treatment for DBPs Control Sorption Powder activated carbon (PAC) Granular activated carbon (GAC) Synthetic resins Oxidation/reduction Ozone Advanced oxidation processes (AOPs) Ozone/hydrogen peroxide Ozone/UV radiation 48

49 Enhanced coagulation The coagulation process was optimized by the selection of coagulants and coagulant aid rather than by adjusting the ph value because it is expensive to adjust the ph to acidic conditions where the source water has high alkalinity of 150 to 200 mg/l. Raw water Flocculation Sedimentation Filtration 49

50 Ozonation Benefits Adequate disinfection Reduction of chlorine or chloramine dosage Reduction of some DBPs: THMs, HAAs, and HANs Very small THM formation when applied with chloramine Problems Increase of some DBPs: chloropicrin, chlorinated hydrate and CNCl Reduction with bromide ion resulting in brominated DBPs Increase in biodegradable organic matter Need for identification of DBPs 50

51 Treatment trains used in bench scale experiments Cl 2 gas coagulation Rapid Sand Filter Cl 2 gas ClO 2 gas Enhanced coagulation Rapid Sand Filter Cl 2 gas ClO 2 gas Enhanced coagulation GAC Filter Cl 2 gas O 3 gas Enhanced coagulation Rapid Sand Filter Cl 2 gas O 3 gas Enhanced coagulation GAC Filter Cl 2 gas 51

52 Optimization of Coagulation-flocculation process AP: Anionic polymer. NP: Nonionic polymer. CP: Cationic polymer 52

53 Effect of coagulant aid on the treatment of drinking water 53

54 Comparison among different treatment trains Chlorine dioxide reduces the DBPs formation of about 70 to 79.6% for THMs and 70 to 76.4 for HAAS with respect to the chlorine disinfection. Comparison between Train #1 and Trains #1*, #3 and #3* indicated that much stronger DOC removal was achieved by pre-ozonation prior to coagulation and filtration by using sand filter or GAC filter. This Figure clearly indicate that the effluent from trains #3 and #3* reduced the DOC values by 64 and 70 %, respectively. In addition, ozonation induced increase in DOC removal on coagulation processes UVA254 DOC THMs HAAs Train # 1 Train #1* Train #2 Train #2* Train #3 Train #3* Train 1 [enhanced coagulation by CP and sand filtration]; Train 1* [enhanced coagulation by CP and GAC filtration]; Train 2 [disinfection by ClO2, enhanced coagulation by CP and sand filtration]; Train 2* [disinfection by ClO2, enhanced coagulation by CP and GAC filtration]; Train 3 [disinfection by O3, enhanced coagulation by CP and sand filtration]; Train 3* [disinfection by O3, enhanced coagulation by CP and GAC filtration].

55 Conclusion The studied DWTPs were relatively not very effective in removal of dissolved organic carbon (DOC) since the removal percentages of DOC ranged between 15 and 32 mg/l. The concentrations of THMs in the studied drinking water treatment plants were all below the Egyptian standards for Drinking Water Quality (100 µg/l). The average concentrations of studied HAAs in water DWTPs exceeded the maximum contaminant level of 60 μg/l. 55

56 Conclusion (Cont.) Chlorine dioxide is strong oxidizing agent and reduces the DBPs formation of about 70 to 79.6% for THMs and 70 to 76.4 for HAAS with respect to the chlorine disinfection. However chlorine dioxide represents a potential source of risk for human health due to the introduction of inorganic byproducts such as chlorite (ClO 2- ) and chlorate (ClO 3- ) ions. 2ClO 2 + 2OH - = H 2 O + ClO 3 - (Chlorate) + ClO 2- (Chlorite) Using pre-ozonation/enhanced coagulation/activated carbon filtration treatment train appears to be the most effective method for reducing DBPs precursors and DBPS in drinking water treatment. 56

57 Recommendations & Action 57

58 58

59 What should be taken to achieve the water situation? Applying Integrated Water Resources Management approach through developing governmental and non-governmental Institutions as well as enforcement of laws and legislations. Allocating different conventional and non-conventional water resources (agricultural drainage and wastewater reuse, sea water and brackish water desalination, rain harvesting, flash flood harvesting). 59

60 What should be taken to achieve the water situation? (Cont.) Irrigation improvement and changing crop patterns. Cooperation with the Nile Basin countries Supporting and enhancing the private sector role in water management Pollution abatement as well as preserving water resources 60

61 Drinking Water Resource and Demand The Nile River supplies about 97 % of the annual Drinking water resources in Egypt. The domestic sectors consumes 7bcm 3 /year of the total fresh water supplies. Raw water should have low concentrations of all contaminants and exhibit minimal variability from day to day. By avoiding the contamination of water resource, water treatment becomes easier, less expensive and more reliable. 61