Details methods of domestic wastewater treatment that are especially suitable in developing countries. The emphasis is on low-cost, low-energy, low-maintenance, high-performance systems that contribute to environmental sustainability by producing effluents that can be safely and profitably used in agriculture for crop irrigation and/or in aquaculture for fish and aquatic vegetable pond fertilization. waste stabilization ponds (WSPs), wastewater storage and treatment reservoirs, constructed wetlands, upflow anaerobic sludge blanket reactors, biofilters, aerated lagoons and oxidation ditches.