aeration
bacterium
biology
construction
dirty
drainage
dump
ecology
environment
environmental
factory
farms
flow
garbage
industrial
industry
liquid
pipe
plant
polluted
pollution
processing
purification
purity
recycle
recycling
reduce
sanitary
server
sewage
sewage farm
sewage plant
sewage works
sewerage
sludge
sludgeworks
smell
smelly
system
tank
technology
the city
toxic
unhygienic
urban
waste
wastewater
water