One of the best options for ...

One of the best options for onsite decentralized treatment of domestic wastewater is constructed wetlands. It is a green technology, meaning that is based on the use of plants without using electro-mechanical equipment (maybe only a pump) or chemicals. For such applications it is ideal, since it is simple and very cheap system, especially during the operational phase, with minimum energy consumption. With a proper design, the effluent obtained can be of appropriate quality for reuse purposes, eg, for irrigation. You can replace the septic tanks with constructed wetland system or alternatively the wetland can receive and treat the effluent of the septic tank. Let me know if you need more detailed information.