Elimination of microcystis cyanobacteria (blue-green algae) by an ozoflotation process: a pilot plant study

Abstract

It is now known that since cyanobacteria (blue-green algae) occur in both swimming and drinking water supplies, and lakes and rivers, they represent an increasing hazard to animal life and human population. Moreover, high algal contents pose also a number of operation problems for water purification plants. The objective of the work is to study the elimination of a Microcystis strain of cyanobacateria by the use of an ozoflotation process which associates the oxidizing properties of ozone and the physical aspects of flotation. The functioning and the efficiency of a pilot unit is presented according to such parameters as: ozone dose, flow rate, coagulants and raw water quality. The use of ozone in pretreatment leads to an inactivation of the algal cells. Experiments let us calculate the specific ozone utilisation rate of Microcystis and the [C.t] (ozone concentration, contact time) curve is determined versus algal removal. Under real conditions, a previous coagulation stage is necessary; best results are obtained with ferric chloride. Preozonation is also of influence on the enhancement of the coagulation efficiency. Association of the ozoflotation process and bilayer filtration can solve the algae problems of waters presenting low turbidity and low organic content, and improve water quality.

Microalgae harvesting using ozoflotation: Effect on lipid and FAME recoveries

“…In this ozoflotation process, bubbles of ozone, provided by diffusers, adhere to suspended solids (e.g.microalgae), break the superficial tension, and travel to the upper part of the bulk liquid to be physically separated. There have been previous reports using ozoflotation for microalgae separation in drinking water, to ensure that the toxic metabolites produced by microalgae are oxidised in water for drinking purposes [8], [9]. There is limited literature on the use of ozone for harvesting microalgae.…”

Dispersed ozone flotation of Chlorella vulgaris

“…Betzer et al (1980) determined that ozone-induced flotation produced froth; while the settlement of froth yielded settled sludge with 2-7% w/w solids. Benoufella et al (1994) applied an ozoflotation process to remove Microcystis strain in waters. Biofuel production from algal cells should minimize the addition of chemicals for minimizing contamination.…”

Effects of nitrate on intracellular nitrite and growth of Microcystis aeruginosa

“…Under certain conditions, a combination of high nutrient load and warm, stable conditions, cyanobacteria can grow excessively and form blooms which cause a variety of water quality problems, including toxin production, odors, scums and unsafe drinking water (Paerl 1988;Benoufella et al 1994). Nutrient concentrations play an important role in the growth of phytoplankton, and the nitrogen sources considered most important for the growth of phytoplankton are nitrate and ammonium (Viaroli et al 1995;Herndon and Cochlan 2007).…”