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Forest industry wastewaters are difficult to clean: hydraulic and organic load variations, filamentous bulking or pin-point flocs negatively impact depollution processes. The addition of a fine, mineral, talc-based powder, Aquatal, into the aeration tanks of wastewater treatment plants connected to pulp and paper factories has been successfully tested since end of '97. The first case-study presents full results obtained over a period of 18 months in a 20,000 p.e. plant connected to a paper factory. The mineral powder was regularly added to control sludge volume index, thereby ensuring low suspended solids concentration in the outfluent. Plant operators could easily adapt biomass concentration to match organic load variation, thereby maintaining pollution micro-organisms ratio constant. In a second case study, a trouble-shooting strategy was implemented to counteract filamentous bulking. A one-off, large dosage enabled the plant operator to deal effectively with poor settleability sludge and rapidly control sludge blanket expansion. In both cases, the main common characteristics observed were an increase in floc aggregation and the production of heavier and well-structured flocs. The sludge settling velocity increased and an efficient solid/liquid separation was obtained. After a few days, the mineral particles of Aquatal were progressively integrated into the sludge floc structure. When the mineral powder was added to the activated sludge in the aeration basin, chemical interactions frequently encountered with other wastewater treatment additives did not pose a problem. Moreover, with this mineral additive, the biological excess sludge displayed good thickening properties and dewatering was improved. Despite the addition of the insoluble mineral particles, the amount of wet sludge expelled did not increase. Aquatal offers a rapid solution to floc settleability problems which so frequently arise when physical or biological disorders appear in forest industry wastewater treatment plants.

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The effluent quality of a sewage plant using the activated sludge process depends upon the flocculation efficiency. Intensive research work has been devoted to understanding flocculation phenomena and to correct biological disorders. The addition of very fine but dense mineral particles to the aeration tank immediately improves floc formation and increases the weight of the new flocs created. The first consequence is an effective separation between the solid and the liquid phases in the secondary clarifier. In the longer term, the fine particles improve floc structuring and form stable and strong flocs. This has been demonstrated by sending a modified activated sludge through the high shear strength of pumps and hydrocyclones. The mineral of choice is a natural blend of talc and related minerals. These fine talc particles offer a solution to solve floc settleability problems which so frequently arise when biological disorders appear in waste water treatment plants. Despite the addition of insoluble particles the amount of sludge expelled does not increase. The thickening and dewatering properties are improved.

The effect of adding varying mixtures of talc and chlorite powder to activated sludge in order to improve the settling characteristic has been studied. The powder is found to improve the settling velocity of the sludge, strictly by increasing the average density of the sludge floc aggregate. The settling velocity was measured with a recirculated settling column under different concentrations and turbulence levels. Numerical simulation of a secondary settling tank indicates that adding fine powder will improve the overall performance considerably.

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