WATER CHEMISTRY

WATER CHEMISTRY
Chemistry of Water/Wastewater & Treatment
Marks allocation: 14
Due Date Lecture Week 10 (16th October 2015).
Assignment Requirements: Write a report of ~1200 words in total with photos, diagrams and figures (in an
appendix where appropriate) that addresses ONE of the following issues. (The report should include a title,
table of contents, summary, findings and discussion, page numbers, reference list).

1.
During an extended drought period a regional water authority found that a river used as a source
water for drinking purposes had total dissolved solids (TDS) concentration >1500 mg/L, turbidity <5.0
NTU, DOC at 1 mg/L and colour <10HU. When the drought ended and the river flooded, the TDS
dropped to <150 mg/L, but the turbidity increased to 75NTU, DOC increased to 12 mg/L and colour to
80 HU. You work for this water authority as an engineer/scientist and have been asked by your
operations manager to propose treatment processes for treatment of these two water types to provide
safe clean drinking water for the community. Investigate suitable treatment processes that can be
applied as requested by the operations manager. Describe these in detail and justify your proposed
treatment options. Refer where needed to the Australian Drinking Water Guidelines updated 2013,
Chapter 10 (including Table 10.5 Guideline values for physical and chemical characteristics).
2.
You are assigned to operate a drinking water treatment plant of 280 ML per day capacity. The
source water is from a river that contains a high concentration of dissolved organic carbon (DOC), (13
mg/L) and has a high colour (60 HU) but the alkalinity changes seasonally. In summer to winter the
alkalinity is high (>100 mg/L as CaCO3) and in spring after snow has melted in the mountains and the
water flows into the river, the alkalinity is very low (<15 mg/L as CaCO3). You have available a range of
chemicals to treat the water for drinking water supply including (1) Aluminium Chloro Hydrate, (2)
Poly Aluminium Chloride, (3) Alum (Al2(SO4)3:18H20) (4) chlorine (5) sodium hydroxide (6) calcium
carbonate (lime), and (6) the polymer floc aid: PolyDADMAC. Propose how some or all of these
chemicals could be used to treat the water when it is high in alkalinity and when it is low in alkalinity.
Give reasons for your selection of chemicals. What is the purpose of each chemical you have selected?
If the coagulant(s) you have selected need to be dosed into the raw water at 90 mg/L, calculate the mass
of coagulant that needs to be dosed per day if the plant is operating at full capacity. If the treatment
efficiency to remove DOC is 60% and chlorine needs to be dosed at 1 mg/L for each mg/L of DOC
remaining in the water after treatment, calculate the mass of chlorine that needs to be dosed each day at
the treatment plant.
3.
A domestic wastewater source has 1560 mg/L BOD, 82 mg/L total nitrogen (comprising Total
Kjeldahl Nitrogen (TKN), nitrate and nitrite, and ammonia) and 15 mg/L soluble phosphorus (SP).
These parameters need to be brought to <30 mg/L BOD, < 15 mg/L for total nitrogen and < 2.5 mg/L
SP before discharge to a river. Investigate wastewater treatment methods that could be applied to
remove these pollutants to the levels required or these are minimized. Calculate the percentage removal
required for each pollutant. If the wastewater is to be used for recycled water supply to domestic
households for non-potable use such as watering gardens, toilet flushing, washing of pavements,
investigate what further treatment should be applied.

Make sure that your information is suitably referenced, using the Harvard system
www.unisa.edu.au/ltu/students/study/referencing/harvard.pdf and a comprehensive reference list is
provided in your report. References and referencing do not contribute to your word count but do
contribute to your marks.
Marks: 9 marks for content; 3 marks for citation and referencing; 2 marks for clarity and presentation
Completed assignments (including cover sheets) should be submitted:
Water Chemistry Major Assignment Submission Box, under your Tutor’s name.
Building P. Level 2 Next to P2-49
School of Natural and Built Environments
Mawson Lakes Campus.
Course Co-ordinator: Assoc Prof John van Leeuwen, H3-31 Building H, Mawson Lakes, UniSA.

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