Complex sentence: Small-scale treatment can be done in small ponds if the effluent is given sufficient time to be broken down into harmless nutrients, however, these smaller ponds may have to be divided in much the same manner as septic tanks.
Split into simpler sentences: Small-scale treatment can be done in small ponds if the effluent is given time to be broken into harmless nutrients. However, smaller ponds may need to be divided in much the same manner as septic tanks.