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Sewage treatment using Diatom Algae

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Introduction:

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 nutrient assimilation.

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.

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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.

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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)

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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

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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 8%.

Diatoms can consume N and P faster than other algae.

Diatoms can consume all forms of N like Nitrate , Nitrite, Urea and Ammonia.

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.

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Nulagi Technology:

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 diatoms.

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 by Diatoms.

Using Nualgi we can grow Diatom Algae in tanks, lakes, nalas, canals and rivers.

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 desired.

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.

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Schematic diagram showing diatom algae based sewage treatment using Nualgi

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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 sewage treatment

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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 (cont…)

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Parameters Units Inflow O2 demand O2 production using diatoms

COD mg/l 300 300BOD mg/l 200 200Total Nitrogen mg/l 40 600Total Phosphate mg/l 6 650 Total

500 600

Illustration of Sewage Nutrient levels with COD and BOD content and O2 Demand and O2 generation

using diatoms

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.

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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 Phosphorus.

1,000 kgs of Diatoms consume about 1200 kgs of CO2 and produce about 900 kgs of Oxygen during photosynthesis.

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 Carbon Credits.

Nualgi – Diatom Algae

Phyco-remediation of Sewage

Case Study of use in an underground STP

using

LED lights to grow Diatom Algae

Location: Gated community with about 1200 Apartments in Bangalore.

Background:

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 month.

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.

Raw Sewage

Bar screen

Oil skimmer Equalization tank Anoxic tank Aeration tank MBR tank

Permeate tank

Treated water pump

LED Lights

Nualgi dosage ml/Day 175 25 25 25

Tank volume liters 300000 37800 506000 54000

376000

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.

A BLight provided by LEDs in equalization tank (A) and in the aeration tank (B).

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 photosynthesis

Diatom analysis:

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

Application

frequency

Diatom count

(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

Total 250

Nualgi dosage and diatom count

Benefits noticed since start of use of Nualgi

Aeration Tank:

Quick settling of sludge: Good water clarity Reduced odour Decreased sludge No dead sludge

Equalisation Tank:

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 pm

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

RsOne blower of 22.5 KW 24 hours a day @ Rs 7 per kwh ( 22.5 x 7 x 24 )

3780.00

Motor run for 3 hours only per day ( 22.5 x 7 x 3 )

473.00

Saving per day ~ 3300.00Savings per month 99,000.00

Savings in chemicals per month 11,000.00

Total savings per month 1,10,000.00

Total Savings

Benefit of increase in Membrane life, lower maintenance of blowers, etc., is not quantified.

PARAMETER AS ON 19.9.2015Before use of

Nualgi

AS ON 15.12.2015After use of Nualgi

REMARKS

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

TEST REPORTS

Earlier the Nitrogen level of the treated sewage was high, it has reduced by about 80%.

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Summary:

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 production. 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 commercialization. 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.

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References:

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.

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