One has to guess why septic ...

One has to guess why septic tanks can not be adopted. If the local conditions had been described in more detail, an appropriate treatment and disposal method could have been suggested in more clear terms.

If space on ground is the constraint near the building, it may be possible to find the space away or over the building making use of pumps to transfer the collected sewage.

If the groundwater table is close to the ground, problem will lie not with the septic tank (which can be made watertight) but the difficulty would be with the soak pit. The alternative to soak pit would be soak trench over a field, hich can be constructed at shallow depth below the ground and it would soak the effluent from the septic tank and treat it through soil to a level that would not contaminate the ground water.