Expansion of Water Treatment Plant - Lab Report Example

Expansion of Water treatment plant Expanding the existing water treatment plant to deliver 6.25Ml/d up from 5Ml/dWater is amongst the most important aspects (resources) in human life, plant life and animal life (Hwang 2002). As the population (for humans, animals and plants) increases so does the demand for water (Kaul 2002). Humans use water for various purposes, these include: washing, cooking, sanitation and sewer, drinking, in hospitals and in industries among others (Davie 2002). Due to ever increasing demand for water as a result of population increase, existing water treatment plants are normally overwhelmed, therefore, there is a great need to expand their capacity (Judd 2002). This report, therefore, aims at expanding the capacity of an existing water treatment plant to deliver 6.25 million litres daily up from the existing capacity of 5 million litres per day. Aims/Objectives The main aim of this paper is to expand the capacity of an existing water treatment plant to deliver 6.25 million litres daily up from the existing capacity of 5 million litres per day. Theory of design The following are the most important factors in the expansion of the capacity of the existing water treatment plant in order to meet the desired capacity Mass balance Mass balance principle states that mass of material entering a system is equal to the mass of materials leaving the system (Sincero 2000). It can be expressed mathematically as shown below: Or Pump power consumption Power consumed by a pump pumping water can be expressed as shown below Power in horse power is calculated as follows, Or Backwash water volumes Backwash velocity Other important aspects in this design include: chlorine dosing, alum dosing, filter sizing and clarifier sizing (Tebbutt 1998). Clarifier sizing The area of each new clarifier is calculated as shown in the formulae below Mass balance Mass balance is the application of principle of conservation of mass to physical systems’ analyses (Davie 2002). According to mass balance (in its simplest form), mass of material entering a system is equal to the mass of materials leaving the system (Davie 2002). As for this case, there are two types of materials entering the system namely: suspended solids and water. Therefore, mass balance in this case using these materials is as described below. Mass balance on suspended solids According to mass balance, mass of suspended solids entering the processing steps (system) is equal to mass of solids leaving the system (Mass of suspended solid in final treated water plus mass of sludge) (Kaul 2002). Equation, Figure 1: Schematic mass balance for solids in water being processed For Initial water treatment system Where, T = Raw water turbidity (NTU) H = Raw water colour (Hazen) M = alum dose, mg/l Al And for this case, T = 10 NTU H = 7 Hazen M = 5mg Therefore, Rate of sludge production in grams per m3 of raw water is 38.5g/ m3 that is treated. Rate of sludge production in grams per litre of raw water is calculated as follows, Rate of sludge production in milligrams per litre of raw water is calculated as follows Assuming that sludge was totally dry and all the water was recovered after processing Mass balance principle, Assuming sludge density of 1003 Kg/m3 Therefore, 3.85mg of sludge has a volume of 3.85 X 10-8 m3 Solid and water in final water have volume of Total volume of sludge, water and that of solids in water, Amount of suspended solids in raw water (at the input) Design calculations New net flow = 6.25Ml/d = 6250000 litres per day Old net flow = 5Ml/d = 5000000 litres per day Using mass balance The mass of raw water entering the system per day is equal to the mass of final water leaving the system plus mass of sludge leaving the system per day. Mass of final water leaving the system per = 6250000 Kg (1 litres of water = 1 kilogram). Mass of sludge leaving the system is calculated as follows (assuming that 38mg of sludge is produced per 1 litre of final water), Total of mass of raw water Assuming the density of raw water = 1000Kg/m3 Volume of raw water in litres Feed rate = 6.250241 Ml/d Raw water pump power consumption Power in horse power is calculated as follows, Q = flow rate in gallons per min, H = Total head in feet, WHP = horsepower Q = 72.4 l/s = 1146.6 gal/min, H = 1.2 m = 3.94 feet Therefore, Raw water pump power consumption will be 851watts Alum dosing requirements Raw water feed rate = 6.250241 Ml/d Dosage rate for Dry alum (granular alum) Raw flow rate = 6.250241 Ml/d Required dose to maintain the water quality = 5mg/l Dosage rate for liquid alum (granular alum) Assuming, Specific gravity of alum = 1.3 and %w/w = 49% Clarifier sizing Area Flow rate in each clarifier (they are 4 clarifiers) Hydraulic loading Clarifier area (As) Assuming a pitch (p) of 0.05m Required flow rate = 6.25Ml/d New clarifying area per clarifier Therefore each new clarifier should have an area of 20m2, that is, they should have a dimension of 4m by 5m. The existing clarifiers should therefore be modified to measure 4m by 5m. Filter sizing Assuming Maximum filtration velocity = 5m3/m2/h = 5m/h, and minimum run up time = 24 hours (Hill, 2013). Required capacity = 6.25 Ml/d, and clarified suspended solids = 2mg/l. Required capacity in m3 per day = 6250000/1000 = 6250m3 per day Therefore, Required Filter area, The number of filters in previous plant (retaining the number of filters) The new filters should have areas of 10m2. Therefore existing filters should be modified to have dimension of 2m by 5m. Backwash water volumes Initial backwash velocity Therefore, backwash velocity for the sand = 25m/h For the new system, /h Therefore, backwash pump should be modified or replaced to pump 250m3/h Chlorine Dosing The desired chlorine dose = 1mg/l Flow expected flow rate = 6.25Ml/d = 6250000l/d = 6250000Kg/day Chlorine rate Therefore the new system would have chlorine rate of 6250g/day Process flow diagram showing the processes in the system and flow rates References Davie, T., 2002. Fundamentals of Hydrology. New York: Taylor & Francis. Hill, R., 2013. Lecture notes: Water & Wastewater Treatment. West London: Brunel University West London. Hwang, E. J., 2002. Operational factors of submerged inorganic membrane bioreactor for organic wastewater treatment: sludge concentration and aeration rate. Water, 47(1), pp. 121-126. Judd, S., 2002. Process Science and Engineering for Water and Wastewater Treatment. Comwall: IWA Publishing. Kaul, A. G., 2002. Water and Wastewater Analysis. London: Gautam Koppala. Sincero, A. P., 2000. Physical-Chemical Treatment of Water and Wastewater. Florida: IWA Publishing. Tebbutt, T., 1998. Principles of Water Quality Control. Great Britain: Butterworth-Heinemann. Read More