1. do you need Nualgi?
2. Are diatoms + light (2.6% of the energy that would otherwise be used for aeration) really a substitute for mechanical aeration?

The case study was posted to answer these questions in the affirmative.
You will understand only if you use Nualgi.
Theoretical debates are not of much use.

I'm not convinced the product is proven in this case. Wastewater is high in nutrients and unlike seawater which is iron and phosphate deficient, nutrient deficiency in wastewater would not seem to me to be an issue requiring "supplementation" with Nualgi. Yes indeed, sewage is "high nutrition" (for plants) and is INITIALLY low in chlorophyll. Put it in the sun and it won't be for long.

Anoxic conditions result from bacteria deoxygenating wastewater as they decompose organic matter and consume oxygen in the process. Sewage has a very high oxygen demand, but this is over several days and I'd suggest that 21 hours without aeration after vigorous aeration for 3 hours would not result in anoxic conditions, even without light. I appreciate that diatoms would produce some oxygen under 0.375 watts of LED light per 1000 litres of sewage for two days residence and this is of great interest to me as a method of reducing mechanical aeration. But:
1. do you need Nualgi?
2. Are diatoms + light (2.6% of the energy that would otherwise be used for aeration) really a substitute for mechanical aeration?

Bhaskar, you have answered my previous question, that diatom drymatter production is approx. 162 kg per day (from 600,000 litres influent per day), releasing 192 kg oxygen per day, which is 0.032% of the wastewater. I'd suggest this is not enough to reduce the biological oxygen demand much at all from the sewage influent, which would likely have a 5 day BOD of approx 500 mg/l, to result in effluent with a BOD of only 4mg/l in two days. Something doesn't smell right here.

I like the concept of growing diatoms in effluent. I also like the concept of irrigating plants with effluent... in which case I don't want to remove the nutrients at all but use bacterial slime and aeration to reduce BOD... in the dark. I agree the concept of using light and phytoplankton to reduce the need for aeration has merit, provided there is value in the product (diatoms), a method for harvesting and the post-treatment water quality is suitable for discharge into waterways. Bhaskar, could you tell us more about the fish in the permeate tank? Is their diet diatoms?

You may also want to read this report by DoE of USA
www.nrel.gov/biomass/pdfs/24190.pdf

The close out report published in 1998 summarises 20 years of research into algae.
Diatoms ( and other algae ) and Wastewater treatment are mentioned many times.

This is a summary report of the 13 Ocean Iron Fertilization experiments
www.cbd.int/doc/publications/cbd-ts-45-en.pdf

Iron and other trace metals were used in these experiments in oceans to grow Diatoms, in HNLCs - High Nutrition Low Chlorophyll areas of the Ocean. Sewage too is an HNLC.

Asking questions is fine, but you should do some reading about algae and all the information available before asking questions.

This is not an experiment, it is a normal commercial use of a proven product.

Naulgi is in use for many other applications worldwide, the present STP case study is only to confirm performance in an underground location with LEDs.

The information about other uses are available on various websites:

lake-savers.com/diatoms

nualgilakes.com/
nualgiponds.com/
nualgiaquarium.com/

Diatom growth can be upto 1 gram per liter per day, Oxygen production for 1 gram of Diatoms in 1.2 grams, i.e., 1,200 mg per liter per day. There is plenty of literature on algal growth rates, we do not have to redo all these. In this case we estimate the Diatom growth rate to be about 0.27 grams per liter per day.

Our goal is to oxygenate the wastewater and avoid anoxic conditions, so I am not able to understand your reference to 'deoxygenate' and 'anoxic conditions'.

As much as I'd like to believe this, only a controlled experiment would satisfy me that Nualgi is the reason for N reductions. I ask is there evidence that effluent does not have all the trace elements and micro-nutrients required for good diatom growth and that Nualgi is indeed necessary? The reason for proper experimental design is to distinguish such results from claims that snake-oil peddlers make.

You are claiming that 405 kw hours of blower aeration is avoided with 10.5 kw hours of LED light.... IF you use Nualgi. Can you demonstrate that effluent + Nualgi provides superior diatom growth compared with effluent alone under the same conditions?

In this system residence time is two days. I'm interested in understanding how long it takes to deoxygenate the wastewater during this residence, given that it take about 5 days to reduce BOD by 68% under oxygen-available conditions. Seems unlikely to me that vigorous aeration for 3 hours followed by resting for 21 hours would produce anoxic conditions in the tanks. Thus my scepticism.

This is a commercial use of our product and not a research project.
The customer has not kept a record of the biomass removed, in fact the total amount of sludge has declined and they are very happy about this.

Some N would be escaping as N2 gas, due to the aerobic conditions.

A paper comparing Nualgi with other media is attached.

The fact that Diatoms require trace metals / micro-nutrients is well known, all shrimp hatcheries in the world grow Diatoms using various forms of these. Nualgi is a superior way to achieve the same objective in large tanks. In shrimp hatcheries the largest tanks are about 10,000 liters.

There are thousands of MBR STPs in operation in the world.
If reducing number of hours of aeration alone could achieve the same result, all the users would have done this, the consultants who design the MBR STPs or the operators would have suggested this.

Oxygen is required to treat sewage, to satisfy the BOD and COD, this is known for over 100 years, since after 'the great stink' of London in 1858. en.wikipedia.org/wiki/Great_Stink and en.wikipedia.org/wiki/Biochemical_oxygen_demand

The issue is how to obtain the oxygen in an economical and sustainable manner.

Diatoms produce Oxygen by consuming CO2, N and P.
Electric aerators dissolve atmospheric oxygen and produce CO2 at the power generating plants and do not consume N and P.

About 20 to 25% of the oxygen in the atmosphere is from Diatom Algae that grows in lakes and oceans.

Okay, so the only N removal in this system takes place by removing biomass from the filters? You report a daily sewerage flow of 600,000 litres. How much biomass is removed from the membrane filters?

Two further comments:

1. Please provide published evidence that for diatoms to thrive in effluent, that Nualgi is required.
2. In my view, to be credible (i.e. valid and objective conclusions), your experimental design should have controlled for aeration. Your claims of lower nitrogen levels because of adding Nualgi could alternatively be explained by introducing a resting period (i.e. no aeration for 19 hours per day, followed by 3 hours vigorous aeration). You can only claim that BOTH reducing the aeration from 24 hours per day to 3 hours per day AND/OR adding Nualgi produced those results, nothing more. By resting the effluent the suspended solids would settle out and these results suggest that "tuning" the aeration would vastly improve the performance of the treatment plant without lighting and Nualgi.

In this STP using MBR technology, most of the Diatoms are filtered by the membranes, so the N in them is removed from the water.

If such filters are not used, the treated sewage with Diatom biomass will flow out into a lake or river and the fish in these consume the Diatoms. Where land is available, the STP owner can build a large pond to grow fish and earn money out of sewage.

A file with a long list of papers about Diatoms and Fish is attached.
In nature Diatoms account for about 50% of the photosynthesis in water, they are the main source of food for most fish - finfish, crustaceans like shrimp and oysters, Whales, etc.
This is why growing Diatom Algae is different from growing other types of algae such as Green Algae.

Nualgi is being used since 2005 in sewage polluted ponds and lakes, to keep them clean and well oxygenated and to feed the fish.

Hi Bhaskar,

a question about N being consumed by daitoms.

Diatom Algae consume nutrients, N and P, and produce Oxygen during photosynthesis.

That is one part of the cycle. Although N is consumed in forming diatom biomass, the N is still present in the biomass which will eventually decompose and release the N again. Are your results simply showing the lag (by only measuring nitrate and not measuring the organic N in the diatom biomass contained in that effluent), or is the diatom biomass then being consumed by the fish in the next step, which would retain much of that N in their flesh that could be harvested (i.e. removed from the system)?

cheers
Dean

Algae require light for photosynthesis and they are generally grow in ponds, raceways or photobioreactors. However, we have demonstrated that Diatom Algae can be grown in an underground sewage treatment plant using LEDs as the light source.

The 1 MLD Membrane Bioreactor ( MBR ) technology plant is located in the basement of an apartment complex with about 1200 apartments, population about 5,000. Actual daily flow is 600 KLD.

450 Watts of LED lights were used to grow the Diatoms.

The plant has a 30 HP ( 22.5 KW ) electric aerator. This was earlier being used 24 hours a day. But since use of Nualgi started in September 2015 the usage has been reduced to just 3 hours a day. This resulted in savings of 470 kwhs per day.

The Nitrogen level of the treated sewage was earlier high but this is now lower since N is consumed by Diatoms.

A report is attached.