High rate algal ponds

37 Pages·2016·12.39 MB·English

by  Howard Fallowfield

Community Wastewater Reuse
Adoption of High Rate Algal Ponds for Rural
Wastewater Treatment in South Australia
Professor Howard Fallowfield
Health and Environment Group, School of the Environment, Flinders University,
GPO Box 2100, Adelaide 5001, South Australia
[email protected]
ICE WaRM Webinar August 2016
High Rate Algal Ponds for Rural Wastewater Treatment
• The problem
• The old solutions
– Issues and limitations
• The new solution
– Benefits
2
The Problem
• Wastewater treatment in rural communities.
• No wastewater treatment infrastructure
support from major utilities.
3
Solution (1): On site wastewater treatment
On-site disposal –
‘soakage trench’
Normally 3,000L;
24h detention,
60-70% SS &
30% BOD removed
5
4
Problems with on-site disposal of treated effluent
• Disposal of treated effluent via sub-surface drainage or a ‘soakage
trench’ can be problematic.
– clay soils with low permeability
– pooling of treated effluent resulting in
– greater exposure of resident adults, children and pets to potential pathogens;
– sandy soils – groundwater contamination
• Surface watercourses may also be contaminated from run-off during
periods of heavy rainfall. http://www.waternsw.com.au/__data/assets/pdf_file/0003/59853/Section-10-Absorption-Trenches-and-Beds.pdf
Potential River Murray Contamination
6
Solution (2)
Community wastewater
management schemes
(CWMS)
7
SA: Community wastewater management schemes
Septic tanks on site:
• Anaerobic digestion of organic carbon.
• Solids retained in tank, permits use of small
diameter pipework & infrastructure (lowering cost)
• Local Council maintains septic tanks.
• Very consistent effluent composition from system.
• Liquid phase delivered to treatment lagoons with
long retention times (66d) = large surface area.
66 day retention time
8
Problems with large deep (1.4m) lagoons
Stratification: Dissolved oxygen, temperature and
pH
7.2 7.4 7.6 7.8 8
pH
0
0 6 12 18
Dissolved oxygen (mg/L)
0
24 24.5 25 25.5 26 Temperature (oC)
20
0
20 High treatment efficiency
photic zone
40
20
40
)60
m40
c
h (60 Thermocline
t
p80
e60
D
80
100
80
100 Low treatment efficiency
euphotic zone
100
Sweeney, DG, Nixon, JB, Cromar, NJ & Fallowfield, HJ. (2005)
Water Science and Technology,51, 163-172.
9
Problems with unmixed lagoons (waste
stabilization ponds)
Recirculation
Hydraulic short circuiting
Wind effects
STED Design Criteria, DoH, LGA, 2002
Opportunity for High Rate
Algal Ponds ?
10