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Reducing Urea in Wastewater Treatment: Cutting Urea & DAP by 60% Without MLSS Crash
Updated: 22 hours ago
Overview
Urea and DAP are commonly added to biological wastewater treatment systems to provide nitrogen and phosphorus for microbial growth. But reducing their dosage too quickly can disturb the nutrient balance and affect MLSS. In this ETP, we reduced urea and DAP dosage by 60% while maintaining MLSS stability in the aeration tank. Instead of making a sudden cut, the dosage was reduced gradually while an alternative nutrient source was introduced. This blog explains reducing urea in wastewater treatment, how nutrient balance affects biomass, what operators should monitor during the change, and how wider nutrient support can reduce dependence on conventional urea and DAP dosing.
Table of Contents
Cutting urea and DAP sounded risky.
Both had been part of the ETP's daily nutrient dosing, and the biomass depended on a steady supply of nitrogen and phosphorus. A sudden cut could leave the microorganisms short of nutrients and cause MLSS to fall.
But continuing the same dosing also meant higher chemical use.
So we changed the nutrient programme gradually. The result was a 60% reduction in urea and DAP dosage while maintaining MLSS stability in the aeration tank.
The important part was not simply using less chemical. It was making sure the microorganisms still received the nutrients they needed.
Why Are Urea and DAP Added to an ETP?
Microorganisms cannot live on BOD and COD alone.
They also need nitrogen and phosphorus to grow and reproduce. Industrial wastewater may not always contain enough of these nutrients, so operators commonly add urea as a nitrogen source and DAP as a source of nitrogen and phosphorus.
This forms part of nutrient balance in wastewater treatment.
If nitrogen or phosphorus becomes too low, microbial activity may fall. BOD and COD removal can suffer, and sludge health can change.
This is why reducing urea in wastewater treatment needs to be done carefully.
Why We Did Not Stop Urea and DAP Overnight
One of the first questions was how to reduce urea dosing in an effluent treatment plant without disturbing the biomass.
We did not make a sudden cut.
The existing dose was reduced in stages while the alternative nutrient source was introduced. During this period, MLSS and biological treatment had to be watched closely.
This matters because why MLSS drops after reducing DAP in an ETP can often come down to nutrient shortage. If phosphorus or nitrogen falls below what the microorganisms need, biomass activity and growth can suffer.
A sudden change gives the biological system little time to adjust.
Urea and DAP Were Not Supplying Everything
Urea mainly provides nitrogen. DAP provides nitrogen and phosphorus.
But microorganisms also need smaller amounts of other nutrients.
A micronutrient deficiency in STP or ETP systems may involve iron, zinc, manganese or other elements required for normal microbial activity.
Simply increasing urea does not correct every nutrient shortage.
This was an important part of our approach to nutrient dosing for sludge health. Instead of looking only at nitrogen and phosphorus, we considered the wider nutrient needs of the biomass.
What We Used During the Reduction
We introduced NutriServe N&P Enhancer while gradually reducing conventional nutrient dosing.
It is an algal gel-based nitrogen and phosphorus supplement for ETP and STP biological systems. The formulation contains nitrogen and phosphorus along with micronutrients such as copper, zinc, iron and manganese. It also contains secondary nutrients including calcium, magnesium and sulphur.
The product uses seaweed extract for wastewater treatment as part of its nutrient formulation.
The aim was to reduce dependence on urea and DAP without suddenly removing the nutrients available to the biomass.
How Did We Protect MLSS During the Change?
We watched the biological system rather than focusing only on how much chemical had been removed.
What we monitored | Why we checked it |
MLSS | Checked whether biomass was being maintained |
MLVSS | Helped assess the organic fraction of MLSS |
BOD/COD | Showed whether treatment was continuing |
DO | Checked oxygen available to aerobic bacteria |
Sludge settling | Helped identify changes in biomass condition |
This gave us a better view of MLSS stability in the aeration tank during the transition.
It also helped us judge COD and BOD assimilation improvement without assuming that a stable MLSS number alone meant the biology was healthy.
Can Seaweed-Based Nutrients Support MLSS?
A marine seaweed extract for MLSS growth in the aeration tank can provide nutrients beyond the nitrogen supplied by urea alone.
According to Amalgam Biotech, the marine extract in its formulation provides nutrient sources and supports nitrogen fixation. The product is intended to support microbial growth and BOD and organically bound COD assimilation.
This makes it a natural nitrogen supplement for biological wastewater treatment, but it should not be described as a total replacement for every source of nitrogen and phosphorus.
The actual nutrient demand still depends on the wastewater.
Can Urea and DAP Be Completely Replaced?
When looking for a urea and DAP alternative for biological treatment, complete replacement should not be assumed.
The manufacturer states that NutriServe N&P Enhancer can reduce urea and DAP requirements by 50–75%, rather than claiming that they can always be removed completely.
In our case, the target was a 60% reduction.
The remaining requirement depends on incoming BOD/COD, nitrogen, phosphorus, biomass and plant operating conditions.
This same point applies when searching for a nutrient supplement to replace urea and DAP in an STP.
Why Nutrient Balance Matters More Than the Urea Dose
Good biological nutrient removal in STP and ETP plants depends on microbial activity, and those microorganisms need the right nutrient conditions.
Too little nitrogen or phosphorus can limit biological activity. Excess dosing can waste chemicals and may add unnecessary nutrients to the treatment process.
For nitrogen supplementation in aerobic treatment, the aim should be to match nutrient supply with actual biological demand.
NutriServe N&P Enhancer may be considered where a plant wants to gradually reduce its dependence on conventional urea and DAP dosing while supplying a wider range of nutrients.
Conclusion
Reducing urea in wastewater treatment should never mean suddenly starving the biomass.
Our approach was to reduce urea and DAP gradually while watching MLSS, MLVSS, oxygen, sludge condition and BOD/COD treatment.
The 60% reduction was possible because nutrient supply was changed rather than simply removed.
For operators asking how to reduce urea dosing in an effluent treatment plant, the safer starting point is plant data. Find out what the biomass actually needs, reduce conventional dosing in stages and watch the biological response closely.
That is far safer than making a large cut and waiting to see whether the MLSS crashes.
Amalgam Biotech is a Pune-based manufacturer of bioculture, process additives, and odour control solutions for industrial and municipal wastewater treatment across India and international markets.
Reduce Urea & DAP Without Compromising MLSS
Excessive urea and DAP dosing can increase operating costs while still leaving your biomass deficient in essential micronutrients. A complete nutrient enhancement solution helps maintain stable MLSS, improve BOD/COD removal, and reduce dependence on conventional chemical nutrients.
