wastewater treatment plant based on activated sludge with biological phosphate and nitrogen removal via pre-denitrification. The treatment plant consists of the following subsequent process units; screen, grit chamber, primary sedimentation, anaerobic tank, anoxic tank, aerobic tank, final clarifier and sludge dewatering. After dewatering the sludge will be directly transported to the sludge incineration plant.
The influent flow (dwf) is 30,000 m3/day and the influent BOD concentration is 300 mg BOD/l. The suspended solid concentration in the influent is 150 mg/l of which 40% is removed in the primary clarifier, which agrees with about 20% BOD removal. The sludge yield (Y) is 0.6 kgX/kgBODremoved.
1. Calculate the biomass production (kg biomass per day) assuming all BOD entering the biological process is removed
2. Calculate the primary sludge production (kg per day), but for simplicity neglect the remainder of the suspended solids.
3. The sludge is directly dewatered to a final dry solid concentration of 18%. How much trucks (we are talking about truck transport, thus movements of trucks, not the physical truck itself), that can transport a load of 30 ton, will be needed per year for sludge transport to the incineration plant?
The sludge is directly dewatered to a final dry solid concentration of 18%. How much trucks (we are talking about truck transport, thus movements of trucks, not the physical truck itself), that can transport a load of 30 ton, will be needed per year for sludge transport to the incineration plant? answer
To answer these questions, we need to calculate the biomass production, primary sludge production, and the number of trucks needed for sludge transport. Let's break it down step by step:
1. Calculate the biomass production (kg biomass per day):
The influent flow rate (dwf) is given as 30,000 m3/day, and the influent BOD concentration is 300 mg BOD/l. To calculate the biomass production, we need to determine the mass of BOD entering the biological process.
First, convert the influent flow rate from cubic meters to liters:
30,000 m3/day = 30,000,000 liters/day
The mass of BOD entering the biological process per day can be calculated as follows:
Mass BOD/day = dwf (m3/day) x BOD concentration (mg BOD/l) x 10^-3 (to convert mg to kg)
Mass BOD/day = 30,000,000 liters/day x 300 mg BOD/l x 10^-3
Mass BOD/day = 9,000 kg BOD/day
Since all BOD entering the biological process is assumed to be removed, the biomass production will be equal to the mass of BOD removed:
Biomass production (kg biomass/day) = 9,000 kg BOD/day
2. Calculate the primary sludge production (kg per day):
The primary sludge production can be calculated considering the removal efficiencies in the primary clarifier.
The suspended solid concentration in the influent is given as 150 mg/l, of which 40% is removed in the primary clarifier. Since the primary sludge production is a fraction of the removed suspended solids, we need to calculate the suspended solids (SS) removed in the primary clarifier:
SS removed/day = dwf (m3/day) x SS concentration (mg SS/l) x removal efficiency
SS removed/day = 30,000,000 liters/day x 150 mg SS/l x 40%
SS removed/day = 1,800,000 mg SS/day
The primary sludge production can be calculated by multiplying the removed suspended solids by the sludge yield (Y):
Primary sludge production (kg/day) = SS removed/day (mg/day) x Y (kgX/kg SS)
Primary sludge production (kg/day) = 1,800,000 mg/day x 0.6 kgX/kgSS
Primary sludge production (kg/day) = 1,080,000 kg/day
Note: The question states to neglect the remainder of the suspended solids for simplicity, so we directly consider the removed suspended solids in this calculation.
3. Calculate the number of trucks needed for sludge transport:
The final dry solid concentration of the dewatered sludge is given as 18%. To calculate the weight of sludge to be transported per day, we need to convert the primary sludge production from kilograms to tons:
Primary sludge production (tons/day) = Primary sludge production (kg/day) / 1000 (to convert kg to tons)
Primary sludge production (tons/day) = 1,080,000 kg/day / 1000
Primary sludge production (tons/day) = 1,080 tons/day
To calculate the number of truck movements per year, we need to consider the load capacity of each truck and the number of working days in a year:
Number of truck movements/year = Primary sludge production (tons/year) / (Truck load capacity (tons) x Working days/year)
Truck load capacity is given as 30 tons, and let's assume there are 365 working days in a year:
Number of truck movements/year = 1,080 tons/day / (30 tons/truck x 365 days/year)
Number of truck movements/year = 1,080 tons/year / 10,950 tons/year
Number of truck movements/year = 0.0988 truck movements/year (approximately)
Therefore, you would need approximately 0.1 truck movement per year (or roughly once every 10 years) for the sludge transport to the incineration plant based on the given parameters.