Water, Sewage & Effluent March April 2019 | Page 17

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IAPS (and variations thereof) have been recognised globally as a contemporary WWT
technology and has been implemented at pilot, demonstration, and full commercial scale
— like the Moundville Wastewater Treatment Lagoon in Hale County, Alabama, US.
Water Sewage & Effluent March/April 2019
15
costs, together with climate change,
rules out the possibility of a second
‘green’ revolution driven by more fossil
fuel fertiliser and fresh water (irrigation).
To fill this gap, community households
and particularly those in peri-urban
areas will have to progressively produce
and preserve more of their own; hence
a focus on implementation of integrated
algal pond systems (IAPS).
The use of ponds provides the most
cost-effective small- and large-scale
reactors for solar-driven waterborne
sewage treatment and for the recycling
of water, energy, and nutrients. IAPS
represent an amalgamation of anaerobic
and aerobic biological processes that
comprise: (i) advanced facultative pond
(AFP) which incorporates a fermentation
pit or in-pond anaerobic digester (IPD);
(ii) high-rate algal oxidation ponds
processed into an organic high nitrogen
containing liquid fertiliser for crop
production and high value horticulture.
As mentioned previously (Water
Sewage & Effluent, Jan/Feb 2019),
the peri-urban space is ideal for
implementation
of
wastewater
treatment and co-product beneficiation.
Sufficiently small so as not to adversely
impact the region while providing a
sanitation amenity IAPS in addition,
delivers water for irrigation, biomass
for downstream processing, and
biogas for heat and power. Peri-urban
environments are considered zones
of transition between rural and urban
and present the ideal location to
demonstrate technologies as projects
that effect sustainable service delivery
and bolster community resilience. It is
within these zones that full integration
of the water, energy, food, and land
nexus can be realised to ensure among
others, food security.
Here, Professor Keith Cowan and
Richard Laubscher of the Institute for
Environmental Biotechnology, Rhodes
University (EBRU) recount challenges
faced during implementation of partial
and fully funded IAPS projects. None of
the projects proceeded beyond design
stage, which highlights the need for an
appropriate framework and action plan
for implementation of demonstrator
technologies in South Africa.
innovations
(HRAOP); (iii) algal settling ponds (ASP);
and (iv) drying beds. In the AFP, the
innovative design of the digester ensures
complete breakdown of biodegradable
solids, including parasites (for example
helminthic ova and worms), which
therefore eliminates the need to heat the
pit or to handle and dispose of sludge.
In addition, heavy metals remain in
the fermentation pit and are typically
precipitated as metal sulphides and/
or insoluble salts. The bottom layers of
the AFP are anaerobic and/or anoxic
and are overlain by oxygen-containing
layers rich in algae and bacteria. These
microorganisms sequester CO 2 , and
oxidise residual methane, hydrogen
sulphide, and nitrogen, produced during
fermentation. The IPD thus produces
a superior biogas with a methane
content >80%. Excess effluent from
the AFP flows into a series of HRAOP
where it is subjected to photosynthetic
oxygenation. Under optimal conditions,
most of the dissolved nutrients are
assimilated into a biomass (equivalent to
mixed liquor suspended solids, or MLSS).
At hydraulic retention time of six days,
complete disinfection is accomplished
through elevated pH and oxygen, and by
exposure to UV radiation from sunlight,
even in winter. The biomass (or MLSS)
produced in the HRAOP is easily and
continuously removed by passive
settling and the resultant slurry dried, or
Professor A Keith Cowan is a director at the Institute for Environmental Biotechnology,
Rhodes University (EBRU) and principal investigator. Richard K Laubscher is a
research officer at EBRU.
About the authors