Use composting toilets
Materials that are flushed down the drain are pumped to a sewage treatment plant where additional energy is used before the “treated” water is released to a surface water body (river or lagoon normally). Composting toilets decompose the waste on site. The decomposed material can be used as fertilizer, just not on food crops.
Available at select plumbing or hardware stores. May need to special order or order on-line. In a composting toilet, waste breaks down aerobically in a controlled process. Sawdust or peat moss may be added to aid decomposition and control odors. High temperatures of composting kill bacteria. Used in National Parks, some homes and businesses.