bengaluru city development minister k j george on thursday said the mandatory installation of sewage treatment plants stp in apartments with 20 units is only for buildings that have come up after february 2016 when the rule was introducedresidential apartment blocks constructed prior to february 2016 will be exempted from the bangalore water supply and sewerage board bwssb rule he saidreplying to a question in the legislative council from chowda reddy of jds george said apartment buildings that do not require stps but have been penalised by bwssb will be reimbursed by way of adjusting the penalty amount against future water billsthe existing rules mandate that buildings with 50 apar tments commercial space of 2000sqft and educational institutions of 10000sqft have to set up stps the strain on the underground drainage system ugd from new apartments commercial complexes and education institutions cannot be ignored hence the rules have been amended to make new ventures install stps the old apartment blocks with 20 units or less and educational institutions with 5000sqft will be exempted from the amended laws he saidas an incentive to old apartment blocks and educational institutions the minister said the state will consider a 30 rebate on the sewage cess levied if they decide to set up stpsbellandur lake to be cleaned in two phasesgeorge told congress p r ramesh that the government will clean bellandur lake in two phases under the first phase the government has undertaken deweeding and the second phase will see the wetlands being developed he saidgeorge said a 100 mld sewage treatment plant will be set up to treat water before it is released into the lake he said the tenders were in the final stages