TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Process: The solids are separated from the suspending reaction liquor and are returned to the reaction vessel inlet, after reaction with the bacterial population. The liquor is treated with a denitrifying bacteria in a denitrification tank and the denitrifying biomass is separated from the supernatant liquor. The supernatant liquor is then clarified by adsorption unit and at least a portion of the separated biomass is returned to the denitrification tank. The balance of the denitrification tank solids is returned to the reaction vessel inlet. The oxygen level is maintained at less than 1 parts per million (ppm) in the denitrifying step. The phosphates and heavy metals are removed from the supernatant liquor by adsorption. The supernatant liquor is contacted with an adsorption filter.Preferred Conditions: The level of dissolved oxygen in the reaction vessel mixed liquor is at least 3 ppm. The suspended solids in the reaction vessel mixed liquor is less than 10000 mg/l, preferably 6000-9000 mg/l. EXAMPLE - A blended sludge was prepared as a slurry at 2-5% solids, screened and passed to a pre-contact tank where it was further diluted to bring the chemical oxygen demand to 1000-7000 mg/l. The slurry was intimately mixed with the returned sludge from the primary clarifier. The residence time within the pre-contact tank was 0.25-1 hours. The liquor overflowed to a reactor. Once in the reactor, the liquor contacted the bacterial species which feed on dissolved, colloidal and suspended organic matter. The aerator within the reactor introduced air into the reactor and also functioned as an excellent mixing system which allowed the bacterial species to have a ready supply of oxygen, thus allowing rapid respiration and bacterial growth. The liquor from the reactor after appropriate residence time overflowed into a primary clarifier of inclined plate design and settled. The settled sludge was returned to the reactor. The supernatant liquor, containing any unoxidized biological oxygen demand plus the nitrate, phosphate and any heavy metals in solution overflowed into the denitrification tank. The liquor from the denitrification tank overflowed to a secondary clarifier of inclined plate design. This separated the denitrifying biomass from the supernatant treated liquor still containing phosphate and heavy metals. A proportion (5-15%) of the settled biomass was returned to the denitrifying tank. The balance was returned to the pre-contact tank. This assisted the preliminary removal of adsorbed nitrate from the incoming sludge. The clarified and treated liquor overflowed from the secondary clarifier into a phosphate removal filter. The final effluent was of very high standard, containing low levels of suspended solids and of oxidizable carbonaceous material. The organic content of the sludge was completely destroyed and nitrate and phosphate levels were reduced to those specified by the regulatory authorities for discharge to inland or coastal waters. The heavy metal ions adsorbed or contained within the destroyed sludge were easily and conveniently removed from the effluent liquor. The process was simple and allowed for a fully automatic operation of the plant once the required operational parameters were set.