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Advanced Water and Wastewater Treatment 

Table of Contents

Abstract

Background.

Current Waste water treatment plant assessment (Malabar waste water treatment plant)

Alternative Waste water treatment system using membrane bioreactor (MBR)

Process flow diagram of the proposed alternate treatment plant incorporating MBR process.

Design information of biological treatment process.

Design information of membrane bioreactor

Calculations.

Clarifier Size.

Aeration Requirements.

Water quality characteristics of the current wastewater treatment plants.

Coagulation/Flocculation.

Sedimentation.

Filtration.

Disinfection.

Reverse Osmosis.

Advantages and disadvantages between the MBR and current wastewater

Disadvantages of Membrane Bioreactor

Drinking Water Supply Augmentation.

Conclusions and Recommendations.

References.

Abstract on Waste Water Reuse Process Design

The Malabar Wastewater Treatment plant is the biggest waste water treatment plant in Australia, treating 635,000 properties that covers an area of 500 km2. The capacity of Malabar waste water treatment plant is 470ml/day. The area of catchment range from Malabar to Blacktown and south to Campbelltown. It has been operating since 1992.

Membrane bioreactor (MBR) employs biological waste water treatment in combination with membrane processes such as ultrafiltration or microfiltration. Membrane bioreactors have many advantages over conventional bioreactors because they required less space, the quality of effluent produced by these reactors is high and they can be easily operated.

Background of Waste Water Reuse Process Design

Clean water is essential for everyday life. Waste water consists of substances that include food scraps, soaps, oils, chemicals and human waste. The waste that produce from domestic water use: showers, toilets, bath tubs, wash basins, sinks and washing machine. Industries and organizations also produce huge quantities of waste water that must be cleaned properly. In waste water treatment, concentration of specific pollutants are reduced to specific level so that they could not harm the people and environment. Waste water is composed of waste water and suspended solids. Several processes are applied to waste water treatment. ("Wastewater", 2020)

Current Waste Water Treatment Plant Assessment (malabar Waste Water Treatment Plant)

The Malabar Wastewater Treatment plant is the biggest waste water treatment plant in Australia, treating 635,000 properties that covers an area of 500 km2. The capacity of Malabar waste water treatment plant is 470ml/day. The area of catchment range from Malabar to Blacktown and south to Campbelltown. It has been operating since 1992.

Located in Malabar catchment, the Malabar Wastewater Project covers an area of approximately 27 km2. Currently, 29% of the total population of the Malabar catchment are provided with sewerage facilities. The present sewerage systems of Malabar such as Arima WWTP, Malabar WWTP, Greenvale WWTP and La Horquetta Lift Station needs repair or they are abandoned ("WASA Multiphase Wastewater Rehabilitation Program - Malabar Wastewater Project Details", 2020).

In order to separate suspended and colloidal solids from sewage, the Malabar process uses magnetite particles and inorganic coagulant. Large surface area is presented by magnetite particles in order to enhance adsorption of sewage particles on its surface. There is no long flocculation time in this process plant.

Alternative Waste Water Treatment System Using Membrane Bioreactor (MBR)

It is considered as top priority to develop Malabar catchment as the catchments drain into the Caroni River. The Caroni Water Treatment Plant provides a portable water to 67% of the population. It is expected that the treated effluent from Malabar waste water treatment plant will water quality standards. It is planned that the treated effluent from waste water treatment plant would be discharged into to creek, draining into Caroni Rivers. The project consists of

  • Construction of a new Wastewater Treatment Plant with capacity 40 ML/d in order to fulfill the needs of year 2035. The projected population of 2035 is 108,630.

The current Malabar WWTP, Arima WWTP and few other waste water treatment plants installed by housing developers will be replaced by new Malabar waste water treatment plant. The new plant will be constructed in a green field site in the east of Peytonville.

The current Malabar WWTP will treat water continuously till a new plant is constructed.

The unit processes for construction of new WWTP are as follows

  • Influent Pumping station (The pumping station will have the capability to handle peak wet weather flow (PWWF) of 189 ML/d)
  • Septage Receiving Station
  • Fine Screening and grit removal facilities (The fine screening and grit removal facilities will have the of handling peak wet weather flow (PWWF) of 189 ML/d)
  • Bioreactors or activated sludge aeration
  • Secondary treatment (the secondary treatment is planned to handle normal flow of 40ML/d and peak flow of 110 ML/d)
  • Storm Water Storage (the flow that is unable to handle by secondary treatment is stored in storm water storage until secondary treatment will have the capacity to handle it)
  • Return Activated Sludge (RAS) Pumping. The unit processes to treat activated sludge are
  • Waste Activated Sludge (WAS) pumping
  • WAS Dewatering (belt filter press and gravity belt thickener)
  • Solar drying (after activated sludge treatment, waste solids are dewatered, solar dried and they are stabilized in greenhouses. Waste solids are disposed at landfills following drying)
  • Disinfection

Treated effluent will be discharged to a creek located south of the proposed site and finally drains into the Mausica and then Caroni River ("WASA Multiphase Wastewater Rehabilitation Program - Malabar Wastewater Project Details", 2020).

Process flow diagram of the proposed alternate treatment plant incorporating MBR process

The flow sheet incorporating membrane bioreactor for waste water treatment is as follows

Design Information of Biological Treatment Process

The design information for conventional biological treatment process is as follows

a. Design Raw Sewage Load (Flow and Strength):

Average Dry Weather Flow (ADWF): 20 ML/d

Peak Dry Weather Flow (PDWF): 1,000 m3/hr

PWWF/ADWF: 3:1

Chemical oxygen demand (COD) (mg/L): 550

BOD (mg/L): 275

SS (mg/L): 250

VSS (mg/L): 212

TKN (mg/L): 55

Ph 7.3

TDS: 250 mg/L

b. Design Operating Conditions:

Liquor Temp: 20oC

Solids Retention Time (SRT) in winter: 15 days

Aerobic SRT in winter: 10 days

Maximum RAS flow: ADWF ratio: 1.0

Maximum ML recycle flow: ADWF ratio: 4.0

Dissolved Oxygen in aerobic zone: 2 mg/L

Maximum MLSS at design SRT: 3,500 mg/L

Reactor Depth: 4.5m

Max solids flux on clarifier: 7 kgSS/m2/hr

Number of clarifiers: 2

c. Waste Activated Sludge (WAS) Production:

Yield at design SRT: 1.0 kgSS/kgBOD applied

d. Aeration Requirements:

Average Oxygenation (AOR): 1.6 kgO2/kgBOD

Peak to average AOR ratio: 1.4

Type of Aeration: Fine Bubble

Aeration Alpha Factor: 0.65

Beta Factor: 0.97

DO @ saturation at 760 mm & 20oC: 9.02 mg/L

Aeration efficiency: 3.5 kgO2(SOR)/kWh

Design Information of Membrane Bioreactor

The design information for membrane bioreactor is as follows

a. Design Raw Sewage Load (Flow and Strength):

Average Dry Weather Flow (ADWF): 20 ML/d

Peak Dry Weather Flow (PDWF): 1,000 m3/hr

PWWF/ADWF: 3:1

Chemical oxygen demand (COD) (mg/L): 550

BOD (mg/L): 275

SS (mg/L): 250

VSS (mg/L): 212

TKN (mg/L): 55

pH 7.3

TDS: 250 mg/L

b. Design Operating Conditions:

Solids Retention Time (SRT) in winter: 15 days

Aerobic SRT in winter: 10 days

Maximum ML recycle flow: ADWF ratio: 4.0

Dissolved Oxygen in aerobic zone: 2 mg/L

Dissolved Oxygen in membrane zone: 6 mg/L

Maximum MLSS at design SRT: 10,000 mg/L

Reactor Depth: 4.5 m minimum

Membrane flux rate: Average: 20 L/m2/hr

Membrane flux rate: Peak hourly: 40 L/m2/hr

Membrane module area: 50 m2

No of modules per cassette: 32

Membrane area per cassette: 1,600 m2

Cassette dimensions (m): 2 (H) x 0.7 (thickness) x 4 (L)

c. Waste Activated Sludge (WAS) Production:

Yield at design SRT: 1.0 kgSS/kgBOD applied

d. Aeration Requirements:

Average Oxygenation (AOR): 1.6 kgO2/kgBOD

Peak to average AOR ratio: 1.4

Type of Aeration: Fine Bubble

Alpha Factor: 0.55

Beta Factor: 0.97

DO @ saturation at 760mm & 20oC: 9.02 mg/L

Power for flux management air flow: 3 kWh/m3

Water Quality Characteristics of The Current Wastewater Treatment Plants

The water quality characteristics of current waste water treatment involves the following processes

Coagulation/Flocculation

To treat raw water, Ferric Chloride, alum or Lime/or other is added to un treated water. The polymer will be mixed with raw water, forming larger particles when smaller particles of dust are sticked together. Larger particles are called flocs and they can easily be removed by filtration or sedimentation.

Sedimentation

Water moves slowly in sedimentation basins and heavy flocs will settle at the bottom of sedimentation tanks. The flocs at the bottom of sedimentation tank is refer to as sludge. The sedimentation step is not included in direct filtration and flocs are removed only by filtration.

Filtration

In filtration, suspended particles are removed from waste water. The material of filter is sand and gravel or crushed anthracite. Filtration enhances the efficiency of disinfection Backwashing is used to clean filters.

Disinfection

Prior to entering the disinfection system, any bacteria's, viruses and parasites are killed by disinfection. Chlorine is the most common disinfectant.

Reverse Osmosis

In reverse osmosis, water is pushed under pressure through a semi-permeable membrane in order to remove Nacl.

Advantages and Disadvantages Between the MBR and Current Wastewater

Membrane bioreactor is used for treatment of waste water. Membrane bioreactor (MBR) employs biological waste water treatment in combination with membrane processes such as ultrafiltration or microfiltration.

  • The space require by MBR is small as compared to biological waste water treatment methods (Frankel, 2020). They have small foot print.
  • The quality of effluent produced by MBR is high.
  • The bio-treatment of MBR is better than conventional biological treatment of waste water.
  • MBR can be operated easily. The process of MBR is straightforward, however, the science of MBR is complex.
  • MBR are flexible and it can be adjusted to varying loads.
  • Membrane bioreactor system relatively low HRT (hydraulic retention time). The hydraulic retention time of membrane bioreactor system is low (few hours or less).
  • SRT (Solid retention time) in MBR is independent of HRT (hydraulic retention time) ("What are the advantages of MBRs?", 2020).

Disadvantages of Membrane Bioreactor

The main disadvantage associated with membrane bioreactor is the fouling of membrane occurs. As a result, the performance of membrane will reduce. Thus, operating and maintenance cost will increase (Iorhemen, Hamza & Tay, 2016).

Drinking Water Supply Augmentation

These are recommended options for upgradtion of existing waste water treatment plants

Addition of Activated Carbon on the Surface of Filter (Filtration)

After recarbonation, water is sent to filters that remove suspended impurities. Activated carbon is added on the surface of filter for adsorption of contaminants. It can effectively remove certain organics such as unwanted odor and taste, chlorine, fluorine and radon from waste water. But it does not remove metals, inorganic contaminates and microbial contaminants.

Addition of Chlorine as an Disinfectant (Disinfection)

The water is disinfected with chlorine after filtration. Chlorine destroys waterborne pathogens that cause cholera, typhoid fever, dysentery and hepatitis A. Chlorine-based pool keeps water safe by killing waterborne pathogens that cause rashes on swimmers ears, skin and foot.

Conclusions and Recommendations on Waste Water Reuse Process Design

Arsenic and lead content in waste water is not addresses in this design, it must be taken into account while designing the waste water treatment plant.

It is recommended that there is a need of better management to operate this water treatment plant efficiently. All instruments must be available on-site and proper monitoring is necessary.

References for Waste Water Reuse Process Design

 (2020). Retrieved 27 May 2020, from https://www.star-group.com.au/experience/water-treatment-plants/water-projects/malabar-parr-improvement

Frankel, T. (2020). Advantages & Disadvantages Of MBBR Wastewater Treatment. Retrieved 27 May 2020, from https://www.ssiaeration.com/advantages-and-disadvantages-of-mbbr-wastewater-treatment/

Iorhemen, O., Hamza, R., & Tay, J. (2016). Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling. Membranes, 6(2), 33. doi: 10.3390/membranes6020033

Modern Techniques in Water and Wastewater Treatment. (2020). Retrieved 27 May 2020, from https://books.google.com.pk/books?id=tiaS_DRlAJsC&pg=PT78&lpg=PT78&dq=Malabar+waste+water+treatment+plant+flow+sheet&source=bl&ots=DSnEte79q1&sig=ACfU3U08MtpYFG7tsLtK4wQzxfgZBhL0dw&hl=en&sa=X&ved=2ahUKEwjWqo60p9TpAhWxxoUKHbABA8sQ6AEwC3oECAoQAQ#v=onepage&q=Malabar%20waste%20water%20treatment%20plant%20flow%20sheet&f=false

Optimised Biogas Production At Malabar Sewage Treatment Plant. (2020). Retrieved 27 May 2020, from https://www.yumpu.com/en/document/read/10619448/optimised-biogas-production-at-malabar-sewage-treatment-plant

Wastewater. (2020). Retrieved 27 May 2020, from https://www.water.wa.gov.au/urban-water/water-recycling-efficiencies/waterwise-community-toolkit/wastewater

WASA Multiphase Wastewater Rehabilitation Program - Malabar Wastewater Project Details. (2020). Retrieved 27 May 2020, from https://www.wasa.gov.tt/WASA_Wastewater%20Rehab_Malabar2890Details.html

What are the advantages of MBRs?. (2020). Retrieved 27 May 2020, from https://www.thembrsite.com/what-are-the-advantages-of-membrane-bioreactors/

Aeration efficiency: 3.5 kgO2(SOR)/kWh

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