Enhancement of Nitrification/Denitrification in Lagoons Using Algal Biofilms

Report No WSAA 147

March 1999

 

SYNOPSIS

 

Lagoon based treatment plants like Melbourne Water’s Western Treatment Plant have been used successfully across the world to provide low cost effective treatment of BOD and suspended solids. As receiving water impacts are better understood and environmental regulation becomes more stringent these plants are increasingly being expected to provide greater levels of nitrogen removal and particularly to reduce ammonia concentrations in the effluent.

 

This study takes demonstrated enhancement of nitrification on a laboratory scale using attached growth biofilms and operates a pilot scale system for three calendar years to assess the success of practical application of the laboratory scale experiments.

 

The data shows that the use of biofilms moves the activity in the ponds from being water column based to being more based on the area of biofilm which is situated in the photic zone. The overall nitrogen removal achieved by the biofilm ponds however is not significantly different to the pond without substrate.

 

The addition of substrate for attached growth significantly reduces the amount of algae in the water column and provides proportionate reductions in the COD and suspended solids of the effluent compared to the pond with no substrate. It is for this benefit that the use of biofilm systems would seem most appropriate in lagoons.

 

The ammonia removal is found to be dependent on temperature and the influent COD loading and also found to be linked to the chlorophyll concentration. This link needs more investigation to separate the effects of algal uptake from any enhancement of ammonia removal.

 

Principles for choosing a material and developing a concept for a biofilm substrate system for use in a lagoon ponds are discussed and developed.

 

A strong correlation between COD and Turbidity is developed for the pilot data and this also needs to be further investigated for applicability as a control tool.

 

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