NOVELTY - The installation comprises an anaerobic digester (1) for processing a waste material to produce a combustible fuel gas and a digestate slurry, a separator (4) for separating solids from the digestate slurry, an algal biomass production unit (3) for receiving liquid part of the digestate slurry from the separator to promote growth of algae, a steam engine fuelled by the fuel gas, a separation unit for receiving a algal biomass from the algal biomass production unit and for separating water from the biomass, and a furnace for combustion of the separated biomass.    USE - The installation is useful for a treatment of organic waste material such as sewage sludge, farm waste and biomass or process waste such as food processing waste to produce biogas such as methane, where the biogas is useful as fuel in an engine.    ADVANTAGE - The installation ensures economical treatment of the organic waste material with less energy consumption in an environmentally friendly manner.    DETAILED DESCRIPTION - The installation comprises an anaerobic digester (1) for processing a waste material to produce a combustible fuel gas and a digestate slurry, a separator (4) for separating solids from the digestate slurry, an algal biomass production unit (3) for receiving liquid part of the digestate slurry from the separator to promote growth of algae, a steam engine fuelled by the fuel gas, a separation unit for receiving an algal biomass from the algal biomass production unit and for separating water from the biomass, a furnace for combustion of the separated biomass, a unit for conversion of energy from the combustion, and a unit for forming the algal biomass into pellets or briquettes for use as the fuel. The engine drives an electricity generator, and outputs heat and exhaust gas containing carbon dioxide. The heat and exhaust gas are supplied to the algal biomass production unit to further promote the growth of algae. The conversion unit includes a heat exchanger for heating water. The heat exchanger is a boiler for generating steam for supply to the engine. The algal biomass production unit comprises a photobioreactor, a channelled lagoon, and a pond or raceway into which the liquid part of the digestate flows. INDEPENDENT CLAIMS are included for:    (1) a method of treatment of organic waste material; and    (2) a method of algal biomass production.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of an installation.    Anaerobic digester (1)    Biomass production unit (3)    Separator (4)    Dewatering unit (5)    Power unit. (7)