Zoogloeal viscous bulking in a Pinus radiata TMP/ONROMG recycled fibre newsprint activated sludge plant

Abstract

In this study, we showed that bulking in an activated sludge plant treating newsprint mill wastewater was due to Zoogloeal viscous bulking (or hydrous bulking).

At Norske Skog's Albury activated sludge plant (ASP) Zoogloeal viscous bulking appeared as microscopic amorphous dumps and formed a crust on wastewater during secondary clarifibation together'with significant foaming in aeration tanks. Production of foaming polysaccharides/exopolymeric substance (EPS) was confirmed using Methylene Blue stain, whereby dispersed and light blue floc characteristics were observed. The condition resulted in the production of white billowy foam, which adversely impacted on the settleability and dewaterability of ASP sludge.

Zoogloeal viscous bulking can be controlled by reducing the Food/Micro-organism (F/M) ratio, maintaining suitable macro-nutrient (orthophosphate and ammonium; P&N) residuals, limiting growth rates with an anoxic selector after an aerobic selector and/or reducing anoxic conditions preceding an aerobic selector.

At the ASP a COD F/M ratio of 20:1 into Selector 1 resulted in significant Zoogloeal bulking. Controlling Zoogloeal growth rates with an anoxic Selector 2 and maintaining suitable ammonium and orthophosphate levels in both aeration tanks was successful in controlling EPS production, Firm floc characteristics (dark blue and low in polysaccharide) were observed using Methylene Blue staining. Defoamer requirements were reduced by a factor of ten.