1. You are the superintendent of a 10 MGD potable water treatment facility. It has been brought to your attention that your source water is excessively hard. Using a combination of lime (Ca(OH)₂) and soda ash (Na₂CO₃) you will soften the water for use in your distribution system. Chemical analysis of the water revealed the constituent concentrations in the table below. (a) Complete the table below and use the results to (b) sketch a meq/L bar graph that indicates the acid/base balance in the water prior to softening, and (c) calculate the quantity of softening materials required on a daily basis (assume 24 hr operation).

 

	Concentration		Molecular Weight		# of Equiv-alents	Equivalent Weight		Equivalent Concentration		Concentration as CaCO3
CO2	5	mg/L	44	g/mol	2		mg/mol eq		meq/L		mg/L
Ca2+	50	mg/L	40	g/mol	2		mg/mol eq		meq/L		mg/L
Mg2+	6.1	mg/L	24.4	g/mol	2		mg/mol eq		meq/L		mg/L
Na+	23	mg/L	23	g/mol	1		mg/mol eq		meq/L		mg/L
Alkalinity	150	mg/L	100	g/mol	2		mg/mol eq		meq/L		mg/L
SO42-	24	mg/L	96	g/mol	2		mg/mol eq		meq/L		mg/L
Cl-	0	mg/L	35.5	g/mol	1		mg/mol eq		meq/L		mg/L

 

 

1. A conventional surface water treatment plant produces water with turbidity less than 0.3 NTU, pH of 8, and a temperature of 10 degrees C. It has a peak flow rate of 400 m³/day .  The water is treated with chlorine in a 100 meter long plug flow reactor that has a volume of 10 cubic meters. The water is then delivered to the first customer 2 kilometers away through a 30 cm diameter pipe. The residual chlorine at the end of the reactor is 0.8 mg/L and 0.2 mg/L at the customer's house.