TASK3: SEAWATER DESALINATION PLANT DESIGN REPORT (20%)
Submission: UTSOnline dropbox
Due Date: see subject outline
1/ Background (10 marks)
Discuss the importance and related issues of desalination for future water security in Australia.
2/ Desalination Plant Design Assessment (65 marks)
• A process flow chart clearly shows your selected intake design, pretreatment process, RO process, and any other relevant processes.
• A detailed design of the RO process clearly describing key parameters such as types of membrane, number of banks, stages, vessels, elements, and recovery, etc. You can use computer aid design software such as ROSA or any other relevant software. You should also clearly discuss what you have done to optimise the RO process design. How do you ensure that you have satisfied the boron limit of 0.3 mg/L?
• Provide a comprehensive literature review on the impact of brine disposal on cuttle fish. Propose relevant options to mitigate any adverse effects of brine disposal on cuttle fish taking into account both economic and environmental considerations.
3/ Shut-down plant of a desalination plant (25 marks)
• When dam levels rise, the desalination plant needs to be shut down. Provide a shut-down, operation and restarting plan of the desalination plant.
42991 Advanced Water and Wastewater Treatment
Design guide for a wastewater treatment plant
1. Estimate the size of the biological reactor:
The total volume of a biological reactor is the sum of the volume of the anoxic and aerobic zones. The role of the biological reactor in our example is to convert soluble bioavailable carbonaceous nutrients (CBOD) into settleable solids and to convert free and saline ammonia into nitrogen gas via nitrification (conversion of ammonia to nitrate) and de-nitrification (conversion of nitrate to nitrogen gas). Ammonia and most of the BOD is oxidised in the aerobic zone, while nitrate is converted to nitrogen gas in the anoxic zone.
The total volume of the biological reactor (m3) can be calculated by:
𝐵𝑂𝐷 𝐿𝑜𝑎𝑑 𝑆𝑙𝑢𝑑𝑔𝑒 𝑌𝑖𝑒𝑙𝑑 𝑆𝑅𝑇
Daily BOD load (kg/Day) = Average Dry Weather Flow (L/day) x Raw Sewage BOD (kg/L)
Solids Retention Time (SRT) in the reactor (days)
Sludge Yield @ SRT (kg Suspended Solids/kg of BOD)
Mixed Liquor Suspended Solids (MLSS) in the Reactor (kg/m3)
Design Note: By increasing the concentration of suspended solids in the reactor (MLSS) it is possible to reduce the volume of the reactor. However, increasing the MLSS makes it harder to settle out the suspended solids in a clarified which will lead to a breach of the permit limit of 5 mg/L suspended solids in the conventional plant. Consequently, the upper limit in our original EPA design is 3500 mg/L. However, a Membrane Bioreactor MBR, uses a membrane to filter the solids. This removes the limitation on the concentration of suspended solids in the reactor. However, there is a penalty. Increasing the MLSS decreases the transfer efficiency of oxygen from gas to water which increases the power needed to deliver oxygen to the aerobic zone.
The total volume of the aerobic reactor (m3) can be calculated by:
𝐴𝑒𝑟𝑜𝑏𝑖𝑐 𝑍𝑜𝑛𝑒 𝑆𝑅𝑇
The volume of the anoxic zone is simply the total reactor volume minus the aerobic reactor volume.
2. Size the clarifier for the original design and the membrane filtration cell
2.1 Clarifier Size
The surface area of a clarifier is defined by the maximum solids loading rate that allows the suspended solids to settle to a depth below the launders (weirs) where the clarified water is collected. The solid loading rate (or flux) determines the mass of solids that can be applied per square meter of clarifier per hour (kgMLSS/m2/h).
The solids flow onto the clarifier is the product of the maximum flow (per hour) and the
concentration of suspended solids in the mixed liquor (MLSS). That is,
𝑆𝑜𝑙𝑖𝑑𝑠 𝐿𝑜𝑎𝑑 = 𝑀𝑎𝑥 𝑓𝑙𝑜𝑤 𝑥 𝑀𝐿𝑆𝑆
The maximum flow is the sum of the peak wet weather flow (PWWF = (3𝑥𝐴𝐷𝑊𝐹)) and the ratio of the Return Activated Sludge (RAS = (1𝑥𝐴𝐷𝑊𝐹)) flow to the Average Dry Weather Flow
(ADWF). That is,
Therefore, the surface area of an individual clarifier is defined as,
2.2 Membrane Cell Size
A membrane bioreactor uses membrane filters in place of a clarifier to remove the suspended solids from the mixed liquor. Like a clarifier, the amount of membrane area required is determined by a loading rate. However, it is a volumetric loading rate (not a solids loading rate).
The maximum volume that can be processed per square meter of membrane per hour is called the filtrate flux. MBR systems operate at two different fluxes for average conditions and peak conditions. The peak wet weather flux is typically twice the average flux. MBR systems are designed using the peak flux.
Membrane area is supplied by membrane manufacturers in the form of a cassette (or rack). Each cassette is made up of multiple membrane modules. The properties of each manufacturers design differ in terms of the type of membrane and the area per module. The amount of membrane area in an individual module can vary from 20 to 60 m2, while the number of modules per cassette or rack can vary from 10 to 50 depending on the manufacturer.
Therefore the membrane area required is estimated using,
The number of membrane modules needed is simply the total area divided by the area per module (Often this number is rounded up to an integer). The number of cassettes is determined by dividing the total number of modules by the modules per cassette (again rounded up to an integer). The cassettes are placed in a separate water retaining structure. The structure is often divided into zones (each zone has an equal number of cassettes). This allows a group of cassettes to be isolated for cleaning or repair without shutting down the whole plant). To minimise the space required the cassettes are positioned on guide rails fitted to the walls of the structure.
3. What are the additional total power (kW) and specific power (kWh/m3) requirements of the MBR compared with the conventional process?
Approximately 45-60% of the power used in biological nutrient removal plants that utilise a combination of aerobic and anoxic zones for the removal of carbonaceous BOD and ammoniacal nitrogen is consumed in the aeration system.
3.1 Aeration requirements for biological reactor
The amount of oxygen required will vary as a function of the BOD load, the oxygen requirements for nitrification (minus the oxygen recovered as a result of de-nitrification) and the Specific Oxygen Rate (SOR). The SOR is site specific and can be determined experimentally or estimated based on the type of nutrients, the properties of the biomass and physical properties of the liquid phase. These parameters are embodied in the site specific average oxygenation requirements (AOR).
If the site specific AOR is known the specific oxygen rate (SOR) can be calculated using the following equation;
Alpha factor (a) Ratio of oxygen transfer efficiency (OTE) in wastewater to OTE in clean water. This parameter accounts for the effects of aeration type, basin geometry, degree of mixing, and the wastewater characteristics such as the presence of surfactants and the level of suspended solids
Beta (ß) is the ratio of oxygen saturation in wastewater to the oxygen saturation in the wastewater, Cs (wastewater)/Cs(tap water). This term corrects for constituents in the wastewater which impact the solubility of oxygen. DO is the design oxygen level in the mixed liquor.
The oxygen requirements can be calculated using the following; Oxygen requirement = BOD load x SOR
The power requirements can be calculated from the aeration efficiency for the aeration device. Once you have determined the SOR calculate the specific power assuming an efficiency of 3.5 kgO2(SOR)/kWh.
3.2 Aeration requirements for membrane bioreactor
Aeration is required in a membrane bioreactor to supply the microorganisms (same as in a conventional process) as well as maintain flow through the membranes. Because membrane bioreactors operate at higher concentrations of mixed liquor suspended solids the alpha factor (Ratio of oxygen transfer efficiency (OTE) in wastewater to OTE in clean water) is lower. Consequently, if the alpha factor for a conventional wastewater plant with a MLSS of 3500 mg/L is 0.65, the alpha factor in a MBR plant operating at a MLSS of 10,000 mg/L would be around 0.5 (The increased concentration of suspended solids decreases the OTE).
The air used to maintain flow through the membranes is delivered in the form of coarse bubbles. These bubbles rise up the outer surface of the membrane and remove the mixed liquor solids that accumulate on the membrane surface. Coarse bubbles are preferred to fine bubbles, because the wake turbulence created by a larger (coarse) bubble rising through a column of water creates more shear force that can act to remove solids accumulated on the membrane surface.
The amount of air required to maintain flow increases with increasing surface area. Manufacturers will specify the air flow rate required to maintain permeate flow. In this example assume that the membrane air flow rate is 0.35 m3 of air for every square meter of membrane per hour (i.e. 0.35 m3/m2/h).
The power requirements to deliver the air to the membranes can be calculated using the equation in the paper on aeration. Alternatively, we can assume that the power requirements for the coarse bubble aeration system are 3 kWh/m3 of air.
42991 Assignment guidelines
? Margins: 2.54 cm (top and left); 2 cm (right and bottom)
? Use Font: Times New Roman, 11 pt (for text); 12 pt for heading/subsection titles
? Use 1.15 spacing
? Provide a cover page (should contain the subject name and number, Assignment number and assignment name, Name and student number of student, Name of lecturer, Date submitted
? Your paper report should contain the following sections (use section numbers and headings):
? Title page
? Statement of original authorship
? Table of contents
? Executive summary (200-300 words)
? Discussion and other sections
? References (there should be at least 10 references, and fully cited)
? Length: Minimum of 8 pages and maximum of 20 pages excluding the cover page. Maximize the space for each page.
? Insert page number for all pages (except cover page)
2. References should be cited properly inside the main text. You can use any referencing format as long as you are consistent throughout the paper. Provide at least 10 references and at least half should be published in the last 5 years. All used in-text citations should be listed in the References section. You can use Endnote or other referencing software.
3. Use paraphrasing and summarising techniques. Do not directly copy and paste from your references. Avoid plagiarism.
4. Make sure that English has been polished and easy to understand. Read and cite recent papers. Provide sound discussion in your reports.
5. You should input your own analysis and discussions along with cited references.
6. Use figures and tables, but make sure you cite them properly if they are already published. Do not forget to put table and figure captions + the citation.
7. MAKE SURE YOUR ASSIGNMENT IS ORIGINAL. AVOID PLAGIARISM.