A few simple designs for primary and secondary treatment of domestic wastewater for surface application to land:
This uses a pump to raise the primary-treated wastewater and remaining suspended solids/sediment up into elevated vermifilters with the outlet high enough to gravity discharge the treated wastewater to surface irrigation.
Where the wastewater can gravity feed crops no pump is required.
A recirculating pump with a timer pumps the primary treated wastewater from the sump to the top of a secondary vermifilter and via gravity back to the sump. The sump overflows into the pump-out tank with a pressure pump and float switch (or alternatively gravity feeds to surface irrigation). Sumps can also be connected in series, each one with a recirculating vermifilter, to achieve higher levels of treatment.