BPD Presentation

HIGH CONCENTRATION POWDERED ACTIVATED CARBON-MEMBRANE BIOREACTOR (PAC-MBR) FOR SLIGHTLY POLLUTED SURFACE WATER TREATMENT AT LOW TEMPERATURE

Authors : - Cong Mab, Shuili Yu , Wenxin Shi , Wende Tian ,S.G.J. Heijman , L.C. Rietveld

State Key Laboratory of Pollution Control and Reuse, Tongji University, Shanghai 2009, China

School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China

Delft University of Technology, P.O. Box 5048, 2600GA Delft, The Netherlands

SUBMITTED BY:BHUNESHWAR CHELAKNITK Surathkal

1. INTRODUCTION

The focus of this study was on the development of a membrane separation system coupled with high concentration of Powdered Activated Carbon (PAC) and to evaluate the effects on the performance of the system at 10 °C and the membrane fouling.

The some researcher pointed that the nitrification process decreases with increasing temperature. The possible justification for this fact is the reduction in microbial richness caused by the drastic temperature changes.

Performance efficiency, resistance of shock load were all enhanced and chemical irreversible membrane fouling was reduced with increasing dosage of PAC in MBR

PAC are able to provide a high surface area support the microbial attachment and biofilm growth.

Under this condition, mean removal efficiencies of ammonia nitrogen (NH3-N) is 93%, and dissolved organic carbon (DOC) removal is 75%

Nitrification in the filtration tank could start within 19 days and be completed within 35 days at 10 °C during the PAC concentration of Fifty grams per liter.

PAC used with the concentration range 5, 25, 50 and 75 g/l which are having high adsorption capacity

2. MATERIALS AND METHODS

The hollow-fiber membrane module is used which are consist of polyethylene (PE)

The surface area of membrane module is 0.06 m2 (320 fibers with 12 cm in length), a nominal pore size of 0.1 µm, an inner diameter of 0.27 mm and outer diameter of 0.41 mm.

The source water was synthesized by tap water and chemical NH4Cl, humic acid and kaolin.

NaOH, NaClO (Sodium hypochlorite), and citric acid were used to remove the fouling

The influent water having NH3-N, 6–7 mg/L; DOC, 5–6.5 mg/L and pH 6.8–7.4.

1. Raw water tank2. Feed pump3. Membrane module4. PAC5. Vacuum gauge6. Electromagnetic valve 7. Effluent pump8. Electromagnetic valve9. Backwash pump10. Clean water tank11. Air blower12. Air flow meter13. Air diffuser14. Refrigerator 15. Water level controller 16. Water level sensor 17. PLC.

Fig. Experimental Equipment for the high concentration PAC-MBR Process.

3. EXPERIMENTAL SETUP AND WORK

The membrane filtration tank having 2 L of volume .

pump sucked the water from raw water tank and discharged into the filtration tank

Water level in the filtration tank controlled by level controller

Activated carbon submerged into the filtration tank.

The PAC was fluidized by continuous aeration from the air diffuser set at the bottom of the tank at a rate of 5 L/min

Continuous aeration was provided by air diffusers, its avoid high concentrations of PAC accumulating at the bottom of the reactor,

Its also could provide adequate oxygen for microorganisms to grow and generate strong turbulence for membrane scour

A vacuum gauge was set between the membrane module and the suction pump to monitor the trans-membrane pressure (TMP).

The water temperature in the bioreactor was maintained at an average value of 10.0 °C using a water bath cooling by a refrigerator

effluent was drawn directly from the membrane module by using a suction pump.

Another suction pump was used for backwashing the membrane module with collected effluent water.

The system was automatically controlled by a programmable logic controller (PLC) system.

The durations of filtration and backwash were controlled automatically using a timer in the PLC based on time intervals of 28 and 2 min in each cycle.

4. FILTRATION

The membrane separation process is based on the presence of semi permeable membrane.

the membrane acts as a very specific filter that allows water to flow through, while it catches suspended solids and other substances

The constituents of the feed stream are deposited on the membrane surface is called membrane fouling.

Particle separation and water permeation involve various mass transport steps in membrane filtration processes.

Mass transfer can be limited by the attachment, accumulation or adsorption of materials on the membrane surface and within membrane pores

Fouling affects the performance of the membrane either by deposition of a layer onto the membrane surface or by blockage or partial blockage the membrane pores

In general, there are three fouling mechanisms were introduced for membrane filtration that can be applied for MBR

5. MEMBRANE FOULING

1.Pore Plugging 2.Cake Formation 3.Pore Closure

Fig:-Three main mechanisms for membrane fouling

1. Pore plugging: for the case when diameters of particles are similar to those of the pores, particles block the pores.

2. Cake formation: for the case when diameters of particles are bigger than diameter of pores, particles deposit on the membrane surface. This leads to cake build-up (cake formation).

3. Pore closure : when diameter of particles is smaller that diameter of pores, particles could enter the pores. As a result some of the entered particles pass the membrane and some foul inside the pores and reduce the open cross-sectional area for flow.

MEMBRANE FOULING

The membrane cleaning procedure can be achieved by two method physical and chemical

Physical cleaning techniques involve membrane relaxation and backwashing.

membrane relaxation is nothing but a pause of filtration process for a short period.

The backwashing or back flushing is a pumping of permeate again in reverse to the reactor through the membrane.

While the TMP reached at 50 kpa, the membrane module washed with deionized water.

Then it was submerged in 2% NaOH for 4 h, whereafter in 0.5% NaClO for 4 h, at last in 3% citric acid for 4 h and washed with deionized water again.

There was only one chemical cleaning needed in 90 days operation

6. MEMBRANE CLEANING

Clogged membrane After washed with tap water After cleaned with chemicals

MEMBRANE CLEANING

7. RESULTS AND DISCUSSION

7.1 System performance on nitrification

NH3-N, NO2-N, and NO3-N in the influent, effluent and bulk were monitored in PAC-0 MBR.

Here by shown that variation of the concentrations of NH3-N and NO2-N in the influent and effluents at various PAC concentrations 0 , 5, 25, 50 & 75 g/l during the 40 days filtration period

The average concentration of NH3-N in the influent was 6.5 mg/L

Fig:- Ammonia-Nitrogen in the influent and effluent

small differences in NH3-N concentration were observed between the influent and the effluent for both PAC-0 and PAC-5 MBRs

the reduction of NH3-N concentration could be observed when the concentrations of PAC were more than 25 g/ L during this period.

high concentration of PAC provide the more surface area for the growth of nitrifying bacteria

The reduction of NH3-N occurred on day 11, day 19, and day 31 in PAC-75, PAC-50, and PAC-25 MBRs, respectively.

During the day 19, the concentration of NH3-N in the effluent began to decrease, which meant NH3-N started to transfer to another form NO2-N.

After day 25, the removal rate of NH3-N was stable above 90% in PAC-50 MBR, which could be contributed to ammonia oxidation bacteria (AOB) biodegradation.

System performance on nitrification

Fig:- Nitrite in the influent and effluent 50 g/L PAC

NO2-N was neither removed nor accumulated significantly before day 18.

NO2-N concentration increasing gradually from day 19 to day 25.

NO2-N began to accumulate to 5.05 mg/L on day 25, and then decreased to 0.95 mg/L on day 31 and to 0.1 mg/L on day 35.

it could be concluded that nitrification began to start up on day 19 from the operation and was completed on day 35 in PAC- 50 MBR at 10 °C

System performance on nitrification

Fig:-Variation of Ammonia Nitrogen

7.2 SHOCK LOADING EFFECT

The experiment conducted at the shock loading with various PAC concentrations and observe the variations of NH3-N and NO2-N in the influent and effluents

The day 1 is a stable period of time.

When NH3-N in the influent fluctuated from about 6.8 mg/L to about 16.5 mg/L, NH3-N in the effluent almost immediately reduced in PAC-75 and PAC-50 MBRs.

The time when NH3-N in the effluent reduced was delayed for 3 days in PAC-25 MBR and 7 days in PAC-5 MBR.

It accumulated and reduced much faster in PAC-75 and PAC-50 MBRs than in PAC-25 and PAC-5 MBRs, which meant nitrifying bacteria propagated faster

The result showed PAC-75 and PAC-50 MBRs had better resistance of NH3-N shock load than PAC-25 and PAC-5 MBRs.

high concentrations of PAC possibly provided higher specific surface area so the biological reaction rate became higher and better resistance of ammonia nitrogen shock load.

7.3 ORGANIC MATTER REMOVAL

Fig:-Variation of DOC

7.3.1 DOC REMOVAL The influent concentration of DOC ranged from 5.4 to 6.1 mg/L and the average value was 5.8 mg/L.

The average DOC concentration of the effluent in PAC-0 MBR was 4.64 mg/L, which corresponded to the removal rate of 20% by only MF membrane separation

On the other hand, 3.77, 2.9, 1.45, and 1.16 mg/L of DOC in the effluent were observed in PAC-5, PAC- 25, PAC-50, and PAC-75 MBRs, respectively, which implied that the total removal rates were 35%, 50%, 75%, and 80%. respectively

Here by shown that the DOC removal gradually increased with the time

PAC-25, PAC-50,and PAC-75 MBRs did not show fluctuations. Only PAC-0 and PAC-5 shows the fluctuations .

This means that high concentration PAC-MBR process has a larger capacity to buffer a high loading of DOC concentration in the influent and stable and safe effluent performances can be achieved.

7.4 OPTIMIZATION OF PAC DOSAGE

diameters of PAC particles were about 100 times larger than the 0.1 µm membrane pores.

Large PAC particles block the membrane pores , they can deposit on the membrane surface and partially can block the surface pores.

It can be removed by period backwash

Cake layer formed by the organic matter, PAC and biomass

higher PAC concentration rapidly reduced flux at the same trans-membrane pressure (TMP),

In practical operation TMP reached at the 50 kpa, its need to physically and chemical cleaning.

Fig. 5. Flux variation by TMP at various PAC concentrations.

When TMP reached 50 kpa, the flux was optimized 19, 18, 15.5, and 13 L/(m2 h) in PAC-5, PAC- 25, PAC-50, and PAC-75 MBRs, respectively,

Its mean that the increasing the concentration of PAC decreases the flux rate

In practical operation TMP reached at the 50 kpa, its need to physically and chemical cleaning.

cake resistance was higher in PAC-50 and PAC-75 MBRs than in PAC-25 and PAC-5 MBRs

The high concentration PAC was selected for the reason:-1. higher concentrations of PAC (50 and 75 g/L) could work as biological

carrier and provide a suitable living environment for nitrifying bacteria at 10 °C, so they enhanced the activity of nitrifying bacteria in MBR, which resulted in shorting the start up period of nitrification at 10 °C

2. higher concentrations of PAC (50 and 75 g/L) MBRs process provided stable and excellent effluent quality, even when fluctuation in the feed was observed.

In this study the critical flux is an important parameter for the filterability of different MBRs which are generally considered as the flux above which formation of cake due to deposition of particles and colloids on the membrane Surface.

Here the critical flux in PAC-50 MBR was measured to be about 20 L/(m2 h).

Its pointed out that increasing the MLSS decreased the critical flux.

MLSS in PAC-50 MBR was higher than in PAC-25 and PAC-5 MBR, because MLSS was composed of PAC and biomass.

So the critical flux in PAC-25 and PAC-5 were both above 20 L/(m2 h). However, the critical flux in PAC-75 MBR was about 10 L/(m2 h).

MBRs were operated at the flux of 16.6 L/(m2 h).

50 g/L PAC were used because the there were periodic backwash and continues aeration during the filtration time and the cake resistance would be limited.

When PAC dosage exceeded a certain concentration (50 g/L), most of the organic matter would be adsorbed onto the PAC and the blockage the membrane pores.

Thus microorganisms may be exposed to some organic matter with poorer biodegradability.

The addition requirement of the PAC are 11 mg/L every day and it can be operated for a 1 year without trouble.

8. CONCLUSIONS

The results showed that the concentration of PAC at 50 g/L acted as biological carrier was high enough nitrification without initial inoculation could start within 19 days and be completed within 35 days at low temperature (10 °C).

Fifty grams per liter PAC was the optimal dosage in MBR for stable and extended operation.

Under this condition, average removal efficiencies of NH3-N is 93.5%, and DOC is 75% at steady-state period.

These facts suggested that this new type of membrane process could be an alternative technology for SPSW even at low temperature (10 °C).

9. REFERENCES

1. Kim, H.-S., Takizawa, S., Ohgaki, S., 2007. Application of microfiltration systems coupled with powdered activated carbon to river water treatment. Desalination 202 (1–3), 271–277.

2. Kim, H.-S., Katayama, H., Takizawa, S., Ohgaki, S., 2005. Development of a microfilter separation system coupled with a high dose of powdered activated carbon for advanced water treatment. Desalination 186 (1–3), 215–226.

3. Xiang-Juan Gai, Han-Seung Kim, The role of powdered activated carbon in enhancing the performance of membrane systems for water treatment De salination 225 (2008) 288–300

4. Abdullah ali al amri, the performance of membrane bioreactor in Treating high temperature municipal wastewater.March 2010

5. Phan Than Tri, Oily wastewater treatment by membrane bioreactor process coupled with biological activated carbon process. August 2002

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