Water treatment method

1. OXIDATION PONDS

2. INTRODUCTION
There are many innovative biological technologies for the
treatment of wastewaters and sludges.
Four such technologies that have now become widely
accepted worldwide are –
• Stabilization ponds
• Plants & wetlands
• Biological Nutrient Removal(BNR) systems
• Composting

3. INTRODUCTION
A stabilization pond is any natural or man-made lentic
(enclosed) body of water.
In this organic waste is oxidized by natural activity.
These are simply large shallow lagoons enclosed by earthen
embankments.
These are common in areas where land is readily available &
cheap & there is plenty of sunshine.
Also used for initial treatment of strong industrial wastewaters
or for the tertiary treatment of domestic wastewaters

4. They are used to treat a wide variety of wastewaters including
sewage.
They can be operated as either anaerobic- or aerobic-based
systems that can be loosely classified into 3 groups-
Anaerobic ponds or lagoons
Oxidation ponds
Aeration lagoons

5. Oxidation ponds are aerobic systems
The oxygen required by the heterotrophic bacteria is provided
not only by transfer from the atmosphere but also by
photosynthetic algae.
There are 4 different types of stabilization ponds –
Facultative ponds
Maturation ponds
River purification lakes
High-rate aerobic stabilization ponds

6. In facultative ponds the algae use the inorganic
compounds(N,P,CO2) released by aerobic & facultative bacteria
for growth using sunlight for energy.
They release oxygen into solution that inturn is utilized by the
bacteria completing the symbiotic cycle
Oxygen also occurs naturally by oxygen transfer ,which is
increased by turbulence.
There are 2 distinct zones in facultative ponds:
Upper aerobic zone - where bacterial (facultative) activity
occurs.
Lower anaerobic zone – where the solid settle out of suspension
to form a sludge that is degraded anaerobic ally
These ponds have a complex ecology with many predator-prey
association, with phyto- & zooplanktonic forms predominating.

8. Ponds are constructed to a depth of between 1.2-1.8m to
ensure maximum penetration of sunlight, and appear dark green
in color due to dense algal development.
The concentration of algae is measured as chlorophyll a & varies
between 500 & 1500µg/l.
Organic loading is expressed as a surface loading rate either as
kg BOD/Ha/day or gm BOD/m²/day that varies significantly with
temperature.
The maximum loading rates in facultative ponds are very low
compared to other biological systems.

9. The final effluent is rich in algae that have a high BOD (i.e.
upto 70-90% of the total BOD).
Overall facultative ponds achieve a BOD removal of about
50%,however when the algae is filtered out in the laboratory
this rises to >90%.
The BOD contribution of the algae in the effluent can be
approximated as 1mg of BOD for every 35µg of chlorophyll a
present.
The BOD surface loading is calculated using equation –
λs=10 LiQ/Af
Where
λs is the surface loading rate(kg/ha/day)
Li the BOD of the influent wastewater(g/m³)
Q the flow rate(m³/day)
Af the area of the pond(m²)

10. EXAMPLE-
Design a facultative pond for an influent wastewater BOD
of 550mg/l and a flow rate of 120m³/day where the
average temperature is 20̊ C.
(a)The BOD surface loading rate at 20̊ C is 253kg
BOD/ha/day.(BOD Surface loading rate is constant at
different temperatures)
(b) The surface area of the pond required is calculated as-
Af =10LiQ/λs=10*550*120/253=2608.7m²
(c) The Hydraulic Retention Time (HRT) of the facultative
pond фf assuming a depth Df of 1.5m is-
фf=Af*Df/Q= 2609*1.5/120=32.6/day

11. Facultative ponds are generally used in series
after an anaerobic lagoon and both of these
systems are used primarily for the removal of the
organic matter.
The effluent from an anaerobic facultative system
does not produce water that can be safely used for
irrigation, especially in warmer climates, due to a
high level of pathogen contamination.
Removal of parasites (including helminthes) &
other pathogens (bacterial, viral & protozoan),is
significantly enhanced by using maturation ponds
in series after the facultative pond.

12. This type of oxidation ponds is widely used throughout the world
as a tertiary treatment process for improving the effluent quality
from secondary biological processes.
Effluent quality is improved by removing suspended solids,
reducing ammonia, nitrate & phosphate concentration, and by
reducing the number of pathogens.
They are of the same depth as facultative ponds,1.0-1.5m
The retention period is normally 10-15 days
Shorter periods can be used for either suspended solids (4 days) or
phosphate removal (7-10 days).
They are also used to improve the quality of lowland river water
prior to potable water treatment.

13. Maturation & facultative ponds have been used for the
fish production for many centuries.
In Western Europe, roach & carp are the prime species
farmed, with chub & perch to a lesser extent.
The main operational problem is disease due to high
density of fish stocked.
Fish ponds require careful management to ensure that
the rate of organic loading does not disturb the ecological
balance

14. FISH
DAPHNIA
CYCLOPS
PHYTOPLANKTON
ROTIFERS
DIAPTOMUS

15. FISH
ROTIFERS
DIAPTOMUS
CYCLOPS
DAPHNIA
PHYTOPLANKTON
Fig. The effect of over-stocking with fish on the food-web in a fish pond system

16. Diffuse pollution is extremely difficult to control and often results
in serious degradation of water quality, especially in large rivers.
Polluted river can be treated by the development of large
impounded lakes to remove & degrade this residual pollution.
Such lakes are very similar to maturation ponds.
E.g..- 5 such lakes have been constructed on the river
Rhur(Germany) with lake Baldeney, the largest with a retention
time of 60 hours at low flows. The lake provides organic treatment
capacity equivalent to a population of 100,000/day. Upto 170 tones
of phosphorus per annum,together with heavy metals, is removed
by sludge settlement in the lake.

17. The solids are removed from the main body of water by
settlement in the lake & which are subsequently removed by
dredging.
The effect on water quality is quite dramatic with the
suspended solids reduced by 56% & the BOD by 34% overall.

18. -RATE AEROBIC
STABILIZATION PONDS
High rate aerobic stabilization ponds are not designed for optimum
purification of wastewater but for algal production.
These are very shallow (20-50cm deep),with an HRT of 1-3 days,and
are mixed at night to prevent settlement and to maintain aerobic
conditions.
Algae are harvested for biomass or single-cell protein.
Green algae such as Chlorella & Scenedesmus, have a protein
content of 50% (dry weight) compared to 60-70% for the BGA
Spirulina.
It is possible to control the cellular constituents of algae by altering
the growth conditions, for ex- by limiting the nitrogen availability the
protein content of the algae decreases while its lipid content
increases.

19. Light availability is the most critical factor controlling algal growth
& so such ponds are restricted to those areas where there is plenty
of sunshine.
The filamentous algae(BGA) Osciallatoria & Spirulina are
preferred as they are easier to harvest & slightly more digestible
than single-celled algae, such as Euglena & Scenedesmus

20. COOPERATION