Enhancementof Nitrification/Denitrification in Lagoons Using Algal Biofilms

ReportNo WSAA 147

March 1999

SYNOPSIS

Lagoonbased treatment plants like Melbourne Water’s Western Treatment Plant have beenused successfully across the world to provide low cost effective treatment ofBOD and suspended solids. As receiving water impacts are better understood andenvironmental regulation becomes more stringent these plants are increasinglybeing expected to provide greater levels of nitrogen removal and particularlyto reduce ammonia concentrations in the effluent.

Thisstudy takes demonstrated enhancement of nitrification on a laboratory scaleusing attached growth biofilms and operates a pilot scale system for threecalendar years to assess the success of practical application of the laboratoryscale experiments.

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

Theaddition of substrate for attached growth significantly reduces the amount ofalgae in the water column and provides proportionate reductions in the COD andsuspended solids of the effluent compared to the pond with no substrate. It isfor this benefit that the use of biofilm systems would seem most appropriate inlagoons.

Theammonia removal is found to be dependent on temperature and the influent CODloading and also found to be linked to the chlorophyll concentration. This linkneeds more investigation to separate the effects of algal uptake from anyenhancement of ammonia removal.

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

Astrong correlation between COD and Turbidity is developed for the pilot dataand this also needs to be further investigated for applicability as a controltool.

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