NOVELTY - Wastewater is treated by performing anaerobic digestion treatment in a first zone (10), then producing a once treated effluent, and periodically removing a bottom sludge; then performing floating aquatic plant treatment to batches of once treated effluent by growing type(s) of floating aquatic plants (14) on a surface of once treated effluent in a second zone (11) exposed to sunlight and atmosphere, then producing batches of twice treated effluent, periodically harvesting floating aquatic plant biomass, and periodically removing bottom sludge; and discharging batches of twice treated effluent.    USE - Method for treating wastewater (claimed), i.e. one of biodegradable agricultural animal wastewater, biodegradable wastewater, biodegradable municipal wastewater, biodegradable domestic wastewater, and biodegradable industrial wastewater.    ADVANTAGE - The method treats the wastewater in an efficient manner utilizing a natural system that is easy to operate and requires little energy input; and uses batch treatment to the once treated effluent which provides increased process control. The land area and upfront construction cost required for the natural system is minimized (all claimed). The method produces useful by-products, e.g. biogas and floating aquatic plant biomass. The opportunistic collection and use of biogas and floating aquatic plant biomass result in additional benefits. The floating aquatic plant biomass is placed into the anaerobic digestion treatment zone where it is digested to produce additional biogas. The additional biogas produced results in more cost effective biogas capture and shortens the payback period for the biogas infrastructure. Digesting the floating aquatic plant biomass on site in the anaerobic digestion treatment zone also eliminates transportation costs, one of the problems with utilizing floating aquatic plant biomass for the useful purpose. The method and the apparatus eliminate the discharge of animal waste to surface waters and groundwater; eliminate atmospheric emissions of ammonia; eliminate the emission of odor; eliminate the release of disease-transmitting vectors and airborne pathogens; and eliminate nutrient and heavy metal contamination of soil and groundwater.    DETAILED DESCRIPTION - Treatment of wastewater includes:    (A) conveying the wastewater to a first zone (10), where the first zone is of predetermined size and is conducive to anaerobic digestion treatment;    (B) providing the first zone where the wastewater is treated via anaerobic digestion, where a once treated effluent is produced following anaerobic digestion, and where a bottom sludge is periodically removed;    (C) conveying the once treated effluent from the first zone to a second zone (11), where the second zone is of predetermined size, is exposed to sunlight and the atmosphere, and is conducive to floating aquatic plant treatment;    (D) providing the second zone where batches of the once treated effluent receive floating aquatic plant treatment by growing a multitude of type(s) of floating aquatic plants (14) on a surface of the once treated effluent, where batches of twice treated effluent are produced following floating aquatic plant treatment, where floating aquatic plant biomass from floating aquatic plant growth is periodically harvested, and where the bottom sludge is periodically removed; and    (E) discharging batches of the twice treated effluent from the second zone.    An INDEPENDENT CLAIM is included for an apparatus for treating wastewater in a reservoir, comprising a sheet of material (8) which is flexible, impermeable, of predetermined size and disposed in the reservoir; a first conveyor; a second conveyor; a third unit for discharging batches of the twice treated effluent from the second zone. The reservoir is one of an existing anaerobic lagoon, a lagoon (6), a pond, a tank, and a concrete cell.    DESCRIPTION OF DRAWING(S) - The drawing is a cross section view of the anaerobic lagoon.    Lagoon (6)    Sheet of material (8)    First zone (10)    Second zone (11)    Floating aquatic plants (14)