Mitigating rural WWTP impacts: System dynamics modeling of downstream nutrient outputs

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Nutrient Recovery

Background:

• Struvite crystallization recovers nitrogen (N) and phosphorus (P) from wastewater, producing fertilizer.
• The full impact of struvite recovery on nutrient allocation in wastewater treatment plants (WWTPs) is not fully understood.
• Investigating additional benefits beyond fertilizer production is crucial for optimizing WWTP operations.

Purpose of the Study:

• To assess the impact of intentional struvite crystallization on nutrient (N and P) distribution in effluent and biosolids.
• To evaluate the potential of struvite recovery to reduce nutrient loads and improve biosolids quality.
• To quantify changes in nutrient ratios within biosolids for land application suitability.

Main Methods:

• System dynamics modeling was employed using operational data from three activated-sludge WWTPs.
• The model simulated the effects of incorporating struvite crystallization on nutrient outputs.
• Effluent and biosolids nutrient loads and ratios were analyzed pre- and post-simulation.

Main Results:

• Struvite crystallization reduced effluent phosphorus (P) load by 37% to 100% across WWTPs.
• Biosolids P load reductions ranged from 17% to 46%.
• A 37% average increase in biosolids N:P ratio was predicted, with N load reductions below 10% for effluent and 14% for biosolids.

Conclusions:

• Intentional struvite crystallization offers significant P removal benefits, reducing effluent loads and improving biosolids quality.
• The increased N:P ratio in biosolids can enhance land-application potential where P restrictions exist.
• While N recovery is less significant, struvite crystallization reduces post-treatment needs and creates a more valuable biosolids product.