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ENE 483

Fall 2022

Design Project:  MiniDesign3

Due 12 December 2022 by 11:59 PM

The City of Christchurch has been mandated to install fluoridation to the treatment process. Estimates are that this would cost NZ$63M. The reason for this is that Christchurch has 49 pumping stations, each of which would require equipment to dose fluorine into the water.

As such, you have been asked to develop a preliminary for a treatment plant to supplement the (Main) Beckenham Pump Station. The Main Pump Station treats groundwater using UV disinfection. It serves 185,000 people and has an average pumping rate of 0.93 m³/s.  You are to assume that the pumping rate cannot be increased.

You are design a treatment to replace the other 48 pumping stations.  This treatment plant is to treat water from the Waimakariri River.  Your treatment plant is to include: rapid mix for coagulant addition, flocculation, and sedimentation, rapid sand filtration, granular activated carbon adsorption, disinfection, and fluoridation.  

Water Demand

The current population of Christchurch is 402,500 (World Population Review, 2022). The total water demand is 435 L/day/person (this includes indoor, outdoor, and fire flow demands) (Christchurch City Council, 2009).  Peak hourly flow can be estimated equal to 5.3 × average daily flow. Maximum day = 2.2 × average day (Davis, 2020).

As you move forward in your design, you are to use the following flowrates:

	Q-average daily (m3/s)	Q-max daily (m3/s)	Q-peak hourly(m3/s)
2022	1.10	3.53	5.83
2042	1.34	4.05	7.10

Filtration

The treatment plant will use a rapid sand filter system:

The design criteria and sand analysis are given below.

Choose a sand from the table provided that meets the GLUMRB recommendations for the effective size and uniformity coefficient.  Adjust the grain size distribution if the sand does not meet the specification.

Depth of sand = 0.65 m

Filtration rate = 5-10 m/h (recommended ≤ 7.5 m/h)

Sand properties:

Color: light brown to light red
Specific Gravity: 2.65
Hardness: 6.0 – 8.0 on MOH scale
Shape factor = 0.8

Stratified bed porosity = 0.45

Filter properties:

Trial backwash velocity = 37 m/h

Trial gullet width = 0.5 m

Underdrain = 30 cm deep filter block with 1 mm orifice

Gravel support = 45 cm in 4 layers (see Table 11-5 in text)

Surface wash = revolving arms at GLUMRB recommended rate

Backwash duration = 25 min

The following is to be provided to complete this portion of the filter design:

● Clean bed headloss

● Backwash velocity

● Depth of expanded bed

● Number of filter beds

● Area of an individual filter bed

● Depth of filter box

● Gullet dimensions

● Plan dimensions

● Backwash water volume

● Backwash tank volume

Disinfection

Bnm,

Disinfectant	Rate constant
Ozone	8.33 x 10-4 L/mg×s
Chlorine	0.016 min-1
Chlorine dioxide	0.012 min-1

Fluoridation

Fluorine is to be added as fluorosilicic acid, which is available in a 25% aqueous solution.

Determine the

· required dosage of fluorosilicic acid

· dosage to be added

· available fluoride ion in fluorosilicic acid

· mass feed rate

· solution feed rate

This is to be done for both the proposed surface water plant and the Main Pump Station.

Corrosion Control

Estimate the LSI, the CSMR, and the Larson-Skole Index and provide a recommendation whether phosphate addition should be provided for corrosion control.

Microcystin removal

Assuming that the river water is found to contain 54 µg/L of microcystins, an exotoxin produced by cyanobacteria. While there is no MAV for microcystins, the provisional MAV is 1 µg/L. The drinking water health advisory (10-d) for bottle-fed infants and pre-school children is 0.3 µg/L and 1.6 µg/L for school-age children and adults.

Sorption of microcystin to Supersorb activated carbon is modelled by the following Freundlich isotherm: q_e = 4.35C_e^0.24 with C_e in µg/L and q_e in µg/mg.

PAC can be added during rapid mixing or GAC can be added as a cap on top of each filter.

Adsorption using PAC during rapid mix:

Calculate how much PAC must be added (kg/d) to meet the health advisories.

Adsorption using a GAC cap on top of filters

Calculate how long (days) the GAC cap can be run before breakthrough (microcystins conc. > 0.3 µg/L):

· GAC layer = 0.4 m deep

· Density of GAC = 550 kg/m³

· Maximum sorption density is 17 µg/mg

Discuss NZ/Aotearoa drinking water regulations for cyanotoxins.

Process sketch

Include a computer-drafted process sketch for your design (thus far) that shows the major treatment steps, fluid flow, chemical doses, residuals formed, etc. It is not necessary to draw the components to scale; just be sure to clearly show each component and its associated parameters.

Economics

Provide a cost-estimate for the capital and operational and maintenance cost for your entire plant.  You will need to adjust the costs for inflation. Use the information provided in (Qasim et al., 1992), if possible, and update the cost data as directed below.

Discussion of sludge disposal and residual management

Discuss the production of residuals and sludges and options for their disposal. Propose a schematic for treatment (conditioning/dewatering/thickening) of the sludge and filter backwash water.  Discuss a disposal strategy that is consistent with Mātauranga Māori and whakapapa and acceptable to the tangata whenua and tangata tiriti. You do not need to do any additional calculations beyond what is stated above.

Format

Your report should provide the basis for all decisions and recommendation.  It should include process specifications.  Clearly document all calculations and state any assumptions, in an appendix. Show equations in symbolic form first, then provide an example where you substitute in values.

Each interim report should include the following sections:

Cover letter

Cover page

Executive Summary ( Your charge, Results, Recommendations)

Introduction

Appropriate sections

Process diagram showing entire plant from river intake to distribution

Economics for the entire plant

Recommendations

Include all units and unit conversions in your calculations in Appendix. This may be hand-written and scanned.

Report all dimensions in SI units.

¡ Your design must meet specifications in the GLUMRB Standards (2018).

 

Cost of Treatment Processes

Qasim and colleagues (Journal AWWA, 84:8:56-62) estimated the total construction cost (CC in October 1978 US $) as a function of its capacity (x) in m³.

The costs can be updated to the present by taking into account present construction costs as documented in the Engineering News Record’s Construction Cost Index (CCI):

The CCI₁₉₇₈ was 2776. The current CCI is about 13171 (see the Engineering News Record website at http://enr.construction.com/economics/). Note that Qasim and colleagues parsed out the CC into various categories, each of which was adjusted separately. For our purposes, we will use the general CCI to update the full cost. These authors also present the standard method for translating a capital cost to an equivalent annual cost (EAC) using the capital recovery factor (CRF):

Where i is the interest rate per payment period (usually a year) and n is the number of payment periods (usually the design period in years). Note that the CRF is sometimes presented in an alternative equation giving the same value:

So that: