An algal removal using a combination of flocculation and flotation processes.

The paper describes certain facets of the removal of the algae (Scenedesmus quadricauda) from water, using a froth flotation separation method, in conjunction with two types of surfactants, (cetyltrimethylammonium bromide) CTAB and (sodium dodecylsulfate) SDS. A 90% algal removal efficiency was achieved when 100 mg l(-1) of CTAB was used whereas for the SDS solutions, the same concentration gave, by comparison, a very poor algal removal efficiency. An addition of 1 mg l(-1) of a commercial cationic polyelectrolyte, which was the optimal concentration as was evident from the zeta potential and the particle size distribution measurements, prior to the SDS addition resulted in a formation of algal flocs and consequently a substantial improvement in the extent of the algal removal. A 50 mg l(-1) solution of SDS was found to be the optimal concentration to completely remove these algal flocs from water. The amount of water removed along with the algal flocs, produced using 1 mg l(-1) of the commercial polyelectrolyte and subsequently removed using SDS, was comparatively lower than that removed with the algal cells when CTAB was used as the 'collector'. It was generally found, in this study, that an addition of the polyelectrolyte improved the removal efficiencies and the rate of separation and also decreased the amount of the associated water removed along with the algal sludge.

Removal of algae using froth flotation.

This paper describes the removal of algae and attached water using a froth flotation method as a function of the collector type, aeration rates, the pH of the algal suspension and temperature of operation. Dispersed air flotation was used in this study to remove Scenedesmus quadricaudo. The addition of surfactants such as cetyltrimethylammonium bromide and sodium dodecylsulfate increased the aeration rates and reduced the size of air bubbles. Only cetyltrimethylammonium bromide gave high algal removal (90%) whereas sodium dodecylsulfate gave poor algal removal (16%). However, by decreasing the pH values of the algal suspension, it was possible to increase the algal removal efficiency up to 80%. Low temperature operation had an important effect on reducing the rate of algal removal but when the temperature was 20 degrees C or higher there was little change with further temperature rises. The amount of water removed with the algal phase was reduced by using a two-stage flotation process.