Operation of a small scale MBR system for wastewater reuse

Transcription

1 Operation of a small scale MBR system for wastewater reuse K. Azis, Ch. Vardalachakis, P. Melidis and S. Ntougias Laboratory of Wastewater Management and Treatment Technologies, Department of Environmental Engineering, Democritus University of Thrace, Vas. Sofias 12, Xanthi, Greece, e mail: pmelidis@env.duth.gr 1 13 th IWA Specialized Conference on Small

2 Wastewater reclamation and water reuse Introduction Water scarcity and water supply irregularities (The South European countries are often confronted with) Wastewater reclamation and water reuse (a favorable solution to the growing pressure on water resources) The degree of treatment mostly depends by the recommended use of the reclaimed water. Reclaimed water: should be of high quality should meet the strict legislation limits (for agricultural or landscape irrigation, supply of underground aquifers, urban and industrial reuse) 2

3 Wastewater reclamation and water reuse Introduction Concerning the reuse of treated effluents the Joint Ministerial Decree (JMD) /11 indicates the physicochemical and microbiological requirements to be controlled certain constituents of interest have to be monitored and controlled require a sound operation of the secondary BTS monitoring of Escherichia coli and Total coliforms is of great importance Membrane processes are: considered as essentials for the production of high quality effluents suitable for a wide range of reclamation and reuse purposes 3

4 Scope of the study Introduction In this study, the operation of an intermittently aerated and periodically fed external submerged MBR system was investigated in order to assess the reuse potential of the produced permeate. The effluent characteristics were evaluated in comparison to the Greek legislation for the reuse of treated wastewater (Joint Ministerial Decree JMD /2011). 4

5 The SMBRe system Materials and Methods Fig. 1 Schematic diagram of the SMBR system 5

6 The SMBR system operation Materials and Methods operations which were controlled by PLC: time allocation between aerobic and anoxic phase feeding and permeate pump activation feeding time and duration permeate pumping time and duration influent and effluent flow rate settings mixed liquor level control pressure data logging and storing 6

7 The SMBR system membrane characteristics Materials and Methods Table 1. UF membrane characteristics Membrane type Construction material Flat sheet (Microdyn Nadir UP 150) Hydrophilic Polyethersulfone (PES) Pore size 0.04 μm ph range 2 10 Clean water flux 15 L m 2 h 1 Maximum operating pressure operating The effective filtration 5 45 C temperature area +200/ 400 mbar 0.34 m 2 7

8 The SMBR system membrane operation Materials and Methods The membrane module was operated using a filtration cycle consisting of a: back wash and fine bubble aeration period (specific aeration capacity of 0.8 m³/m².h, absolute value of 4.5 L/min). The following cycle program was implemented: 510 sec filtration phase, 30 sec relax phase I, 30 sec back wash (<150 mbar) and 30 sec relax phase II. 8

9 The SMBR system membrane operation Materials and Methods The membrane module was operated using a filtration cycle consisting of a: fine bubble aeration period specific aeration capacity of 0.8 m³/m².h back wash period (<150 mbar) 9

10 The SMBR system biological treatment operation Materials and Methods Intermittent aeration and periodical feeding : divided into one hour cycles each cycle consisted of two phases anoxic (30 min) and aerobic (30 min) periodical feeding at the beginning of the anoxic phase Non aeration Aeration within a short time period Feed Denitrification Nitrification 1 st Phase (30 min) 2 nd Phase (30 min) 1 st cycle (to ensure high substrate availability for denitrification) 10

11 The SMBR system biological treatment characteristics Materials and Methods duration of the study: 190 days inoculated with return activated sludge temperature: 23 25±0.4 ο C dissolved oxygen was measured on line and kept under 0.2 mg/l during the anoxic phase and between 2 and 6 mg/l in the aerobic phase SRT: During the whole experimental period, waste sludge was not removed and the corresponding sludge age (SRT) was equal to the operation day 11

12 The SMBR system biological treatment characteristics Materials and Methods Organic loading rate (L ORG ) of 0.9 ±0.2 g BOD 5 /L.d Nitrogen loading rate (L N,V ) of g TKN/L.d F/M ratio of 0.27 ±0.1 gbod 5 /gvss.d MLSS content was between 4 6 g/l Permeate flux was fluctuated between 4.2 and 13.8 L/m 2 h Permeability was L/m 2.h.bar The respective resistance was m 1. During the experimental period, only a slight TMP increase was observed, with the latter being equal to 142 ± 51.6 mbar 12

13 The SMBR system wastewater characteristics Materials and Methods Mean values of the influent sewage characteristics: total COD, 388 (±196) mg/l biochemical oxygen demand (BOD 5 ), 180 (±64) mg/l total suspended solids (TSS), 201 (±88) mg/l NH 4+ N, 57.7 (±17) mg N/L total Kjeldahl nitrogen (TKN), 78.5 (±22) mg/l ph, 7.31 (±0.23) electrical conductivity, 1,229 (±178) μs/cm Escherichia coli (x10 4 ) cfu/100 ml total coliforms (x10 6 ) cfu/100 ml 13

14 Organic carbon removal Results and Discussion BOD is a main quality parameter characterizing the organic carbon content of the treated effluent BOD restricted irrigation unrestricted irrigation JMD /11 25 mg/l 10 mg/l for 80% of samples Effluent (1 7 mg/l ) median 3.4 ±1.5 mg/l meeting, in any case, the legislation limits for unrestricted irrigation 14

15 Nitrogen removal restricted irrigation Results and Discussion PE< PE> JMD /11 15 mg/l TN 10 mg/l TN NO 3 N eff TKN eff median 0.7 ±0.7 mg/l mg/l The determined effluent total nitrogen concentrations met the legislation limit (lower than 15 mg/l TN) for restricted irrigation, industrial use and groundwater recharge for non potable applications 15

16 Nitrogen removal unrestricted irrigation Results and Discussion PE< PE> JMD /11 15 mg/l TN 10 mg/l TN Extra requirement 2 mg/l NH 4+ N NO 3 N eff TKN eff NH 4+ N eff median 0.7 ±0.7 mg/l mg/l mg/l In the cases of irrigation in nitrite susceptible zones the limit of unrestricted irrigation and groundwater recharge with drilling, the legislation requirements was not met 16

17 Suspended solids and Turbidity Results and Discussion TSS restricted use unrestricted use JMD /11 10 mg/l 2 mg/l in 80% of samples Effluent negligible In this study, TSS were negligible and lower than the effluent quality limits required for unrestricted use (<2 mg/l). 17

18 Suspended solids and Turbidity Results and Discussion Turbidity (NTU) restricted use unrestricted use JMD /11 2 NTU Effluent ( NTU) median 3.26±0.7 NTU Higher than the recommended NTU limits! 18

19 Microbiological aspects Results and Discussion Complete bacterial removal was achieved for the Escherichia coli during the whole experimental period, counting 0 1 cfu/100 ml with a median value of 0.1 cfu/100 ml. These EC numbers complies with the effluent quality standards of the Greek legislation set limits: 200 cfu EC/100 ml for restricted irrigation 5 & 50 cfu EC/100 ml for 80% & 95% of the samples analyzed for unrestricted irrigation 19

20 Microbiological aspects Results and Discussion According to the Greek legislation, TC enumeration is required for unrestricted wastewater reuse. For unrestricted urban and suburban green applications, and groundwater recharge, the TC limits are: 2 cfu/100 ml (for 80% of the samples) 20 cfu/100 ml (for 95% of the samples) 20

21 Microbiological aspects Results and Discussion At the initial stage of the operation, TC removal efficiency was 99.7%, although TC effluent concentration was 6920 cfu/100 ml, which was much higher than the permitted limits. To control this problem, chemical cleaning of the membrane and systematic disinfection of the effluent pipes with NaOCl were implemented: After a short period of time sharp reduction of the effluent TC concentration was observed TC varied between 0 and 10 cfu/100 ml the median value was 4 cfu/100 ml 21

22 Microbiological aspects chlorination Results and Discussion In order to comply with the second requirement of the legislation that sets a limit of 2 cfu TC/100 ml for 80% of the samples analyzed: chlorination of the permeate was implemented using a NaOCl concentration of 2 mg /L. The results showed 100% TC reduction, with the effluent quality meeting the legislation limits for unrestricted use. 22

23 BOD TN Conclusions The results showed a: low effluent BOD concentration (3.4 ±1.5 mg/l), which met the legislation limits for unrestricted use. The effluent total nitrogen (<15 mg TN/L) and ammonia concentrations met the legislation limits for restricted irrigation, industrial use and groundwater recharge for non potable applications. In the cases of unrestricted irrigation, in nitrite susceptible zones the legislation requirements were not achieved. 23

24 TSS Turbidity Conclusions The suspended solids (TSS) concentration comply with the limits for unrestricted use. Permeate Turbidity values were slightly higher than the required limits for unrestricted use. 24

25 Escherichia coli Total coliforms Conclusions The Escherichia coli numbers were within the limits for unrestricted use, while, to meet the legislation limits for Total coliforms, additional measures, such as chlorination, were needed. 25

26 Process modifications Conclusions Modifications in MBR process are necessary to optimize the removal efficiency concerning ammonia and turbidity in order to meet the legislative requirements 26

27 Thank you for your attention 27