Sewage constitutes a major component of wastewater generated everyday in
developing nations like India,.
Untreated or partially treated sewage finds its way to the water bodies
resulting in enrichment of nutrients, leading to eutrophication.
One of the highly significant and rapidly developing methods for sewage
treatment is the use of photosynthesis by growing algae.
Use of algae for municipal wastewater treatment in ponds is well established
(Oswald et al. 1953, Oswald 2003) Algae growth in wastewater treatment ponds
contributes to treatment mainly through dissolved oxygen production and
The release of oxygen from water during photosynthesis provides aerobic
microbiological waste oxidation; and the absorption of carbon dioxide which
also accompanies photosynthesis.
The main advantage algae based systems to conventional systems is removal
of Nutrients, both Nitrogen and Phosphate.
Oswald’s work on sewage treatment using microalgae:
The use of micro algae for the treatment of municipal wastewater has been
subject of research and development for several decades.
In early1950s the first research on using micro-algae for wastewater
treatment was started.
It was demonstrated that algae-based wastewater treatment could remove the
nutrients (e.g., N and P) from settled domestic sewage more efficiently than
traditional activated sewage process, indicating a great potential of algae-based
wastewater treatment system.
The result of such effort is that some commercial technologies and processes
are available in the market such as the Advanced Integrated Wastewater Pond
Systems (AIWPS) Technology commercialized by Oswald and Green, LLC, in
the United States.
Remarks: If Diatoms are grown no excess algae will be left as the diatom
algae are consumed by zooplankton and remaining algae will sink. Other
algae such as Blue Green Algae is NOT consumed by Zooplankton and dead
BGA floats and forms a layer on the water, this causes problems.
The cycle of Oxygen and algal production in sewage
treatment by Photosynthesis (Oswald,1955)
Diatom Algae for sewage treatment :
Growing micro-algae / phytoplankton such as Diatom Algae in the
sewage will enable the nutrients in the sewage to be consumed and
the oxygen produced will satisfy the BOD and COD and provide
Oxygen to fish.
Phytoplankton are the natural food for fish and Diatoms are the
best group of Phytoplankton.
About 50% of the photosynthesis on Earth takes place in water –
lakes and oceans and Diatom Algae account for about 50% of the
algae in water bodies.
Treated sewage with BGA and Green algae can’t be released into
public water bodies.
Diatom can also be grown in underground tanks of sewage
treatment plants with artificial lighting
Advantages of treating sewage with Diatoms:
Diatom Algae are the most prolific micro algae in nature and they grow in
all ponds, lakes, rivers, oceans, aquariums, etc.
They are responsible for about 20 to 25% of all photosynthesis on Earth,
this is more than the share of tropical rain forests ( ~ 18% ) and agriculture
Diatoms can consume N and P faster than other algae.
Diatoms can consume all forms of N like Nitrate , Nitrite, Urea and
Diatoms are best sequesters of CO2 so they can release more Oxygen.
Diatoms can even grow under low light conditions.
Diatoms are the natural food for Zooplankton and Fish, so they are
consumed and hence do not accumulate in the water.
Diatoms are different from other micro algae and aquatic plants, since they
have a silica shell. We have a patented product to use this feature to grow the
Our product is called Nualgi – Nutrition for Algae. It is a liquid and
contains 10 micro-nutrients i.e., Iron, Zinc, Manganese, Boron, etc. required
Using Nualgi we can grow Diatom Algae in tanks, lakes, nalas, canals and
This can be done without constructing any special structure, so there
would be very little capital expenditure.
There is no lead time, so the process can be started or stopped whenever
The sewage polluted water can be converted into bathing quality water,
Grade C and this can be filtered and disinfected for use in industries and
watering gardens, toilet flushing, etc., if not as drinking water.
Schematic diagram showing diatom algae based sewage
treatment using Nualgi
Sewage and Water numbers units Amount
Population Million 20
Water consumption per capita per day liters 250
Water consumption MLD 5,000
Sewage MLD 4,000
Nitrogen in the sewage tons / day 100
Phosphorus in the sewage tons / day 10
CO2 Consumption by Diatoms tons / day 2,000
Oxygen Production by Diatoms tons / day 1,500
Diatom Biomass tons / day 1,250
Fish Biomass tons / day 112
Nualgi dosage liters / day 1,000
Price per liter Rs 5,000
Total Nualgi Cost per day Rs 50,00,000
Nutrient and cost economics of diatom based
Cost per KL of Sewage Rs 1.25
Total Nualgi Cost per year Rs Crores 182
Income from Sale of Fish @ Rs 50 per kg of Fish Rs Crores 200
Net Profit Rs Crores 18
Savings if 3,000 MLD is recycled Rs Crores 1,125
Nutrient and cost economics of diatom based sewage treatment
Parameters Units Inflow O2 demand O2 production
COD mg/l 300 300
BOD mg/l 200 200
Total Nitrogen mg/l 40 600
Total Phosphate mg/l 6 650
Illustration of Sewage Nutrient levels
with COD and BOD content and O2
Demand and O2 generation using
It is possible to produce ALL the oxygen required to satisfy BOD
and COD using the nutrients in the sewage and use of electric
aerators can be eliminated or minimized.
Potential of Nulagi in Numbers:
1 liter of Nualgi can grow upto 1,000 kgs of Diatoms
and these consume about 80 kgs of Nitrogen and 11 kgs of
1,000 kgs of Diatoms consume about 1200 kgs of CO2
and produce about 900 kgs of Oxygen during
The Oxygen produced will reduce the COD and BOD
of the water and CO2 consumption is very beneficial in
reducing the excess CO2 in atmosphere.
Treating sewage using Diatoms may be eligible for
Nualgi – Diatom Algae
Phyco-remediation of Sewage
Case Study of use in an underground STP
LED lights to grow Diatom Algae
Location: Gated community with about 1200 Apartments in Bangalore.
STP is of 1,000 KLD capacity, using Membrane Bioreactor ( MBR )
technology with total tank capacity of 1.3 Million litres. Daily sewage flow is
about 600,000 litres.
Cost of each membrane is about Rs 20 lakhs and there are 5 membranes in
total. Operating expenses to maintain this plant is about Rs.1,30,000 per
Electricity consumption comes to about Rs. 2,50,000 per month.
There are 2 blowers / aerators of 30 HP ( 22.5 KW ) each, one each in the
aeration and equalisation tanks.
The STP is situated in the Lower Basement between F and G Blocks in a
closed room without any sunlight.
Oil skimmer Equalization tank Anoxic tank Aeration tank MBR tank
Treated water pump
Nualgi dosage ml/Day 175 25 25 25
Tank volume liters 300000 37800 506000 54000
STP flow chart along with Nualgi dosage and lighting location
Location of LEDs
LED lights are located on top of equalization tank ( 2 ), anoxic tank ( 2 ),
aeration tank (2), MBR tank ( 2 ) and permeate tank ( 1 ). Lights are fixed
along the sides of the tank just above the top attached to the metal railing
(Photo 1). Each LED is 50 Watts and is kept on 24 hours a day.
Light provided by LEDs in equalization tank (A) and in the aeration
Nualgi Dosage and diatom analysis
Nualgi dosing was started in September 2015.
Nualgi contains 10 micro-nutrients on a Nano Silica base and it causes
Diatom Algae to grow in the sewage.
Diatom Algae consume nutrients, N and P, and produce Oxygen during
Water samples were collected from 5 tanks, Equalization, Anoxic, Aeration,
MBR and Permeate tanks from the top.
The tanks are upto 4.5 meters deep and samples were not drawn from the
bottom of the tanks.
Diatom analysis was done using Taylor et.al. 2007 protocol by cell
counting under microscope (Table.1 above).
3 species of diatoms Nitzschia sp., Cocconeis sp. and Navicula sp. were
found, these are benthic Diatoms.
Location Nualgi dose
ml / day
(cells per ml)
Equalization tank 175 Once a day 200
Anoxic tank 25 Once a day 200
Aeration tank 25 Once a day 700
MBR 25 Once a day 900
Permeate Nil Nil
Nualgi dosage and diatom count
Benefits noticed since start of use of Nualgi
Quick settling of sludge:
Good water clarity
No dead sludge
Active bacteria in the equalization tank;
No methane gas;
No floating material;
Membrane Bio Reactor (MBR):
No choking of MBR
No MBR Noodles formation
MBR cleaning once in 15 to 30 days, instead of 5 – 10 days earlier
MBR life increased
Reduction in chemicals to 500 kgs from 1,200 kgs per month saving ~ INR 11,000
Filter Press 5 Hp Motor:
Motor was not run for 4 months since there is reduced sludge formation.
Savings In Electricity:
Earlier 30 HP blower was run for 24 hours continuously, but since
September 2015, they are being used for only half an hour every 4 hours,
i.e., for 3 hours per day
Benefits noticed since start of use of Nualgi
One blower of 22.5 KW 24 hours a day @ Rs 7 per kwh (
22.5 x 7 x 24 )
Motor run for 3 hours only per day (
22.5 x 7 x 3 )
Saving per day ~ 3300.00
Savings per month 99,000.00
Savings in chemicals per month 11,000.00
Total savings per month 1,10,000.00
Benefit of increase in Membrane life, lower maintenance of blowers, etc., is not
PARAMETER AS ON 19.9.2015
Before use of
AS ON 15.12.2015
After use of
COLOUR <5 <5
ODOUR Agreeable Agreeable
PH VALUE 7.1 6.97
TURBIDITY AS NTU <1.0 <1.0
TDS 625 680
AMMONIA <0.5 <0.5
NITRATE 103.81 23.44 REDUCTION
TOTAL ALKALINITY 154 238
TOTAL HARDNESS 158 172
BOD <3.0 4
COD <10.0 10
Earlier the Nitrogen level of the treated sewage was high, it has reduced
by about 80%.
The negative effects of nutrient overloading from untreated and partially
treated sewage in aquatic systems include nuisance algae, low dissolved
oxygen concentrations and fish kills, undesirable pH shifts, and cyanotoxin
The technical feasibility of many algae based sewage treatment
technologies has been investigated and demonstrated. However, the economic
viability and environmental sustainability remain the key obstacles for their
So with India gearing itself for Swatch Bharath Abhiyan with 11 crore
toilets to be constructed there is an urgent need to develop new technologies to
treat the nutrient in the sewage,
Our Nualgi technology can be a effective solution to make Algae based
sewage treatment cost effective and economically viable.
Diatom based sewage treatment can potentially achieve nutrient removal in
a less expensive and ecologically safer way with the added benefits of resource
recovery and recycling.
1. Nurdogan, Y., Oswald, W.J., 1995. Enhanced nutrient removal in high
rate ponds. Water Science and Technology 31, 33–43.
2. Oswald, W.J., 1987. Sewage treatment in tropical high rate ponds. In:
National Conference on Environmental Engineering, Lake Buena Vista.
3. Oswald, W.J., 1988. Micro-algae and waste-water treatment. In:
Borowitzka, M.A., Borowitzka, L.J. (Eds.), Microalgal Biotechnology.
Cambridge University Press, New York, USA, pp. 305–328.
4. Oswald, W.J., Golueke, C.G., 1960. Biological transformation of solar
energy. Advances in Applied Microbiology 11, 223–242.