Primary water treatment( Continued) Ca(OH)2 and al2(SO4)3 are often added to speed up the sedimentation process 3 Cal(oh)2+ A2(S04 )3>2 Al(OH)3+ 3 CaSo4 Al(OH)3 is a gelatinous precipitation that settles out slowly, carrying suspended material and bacteria with it Oily material floats to the surface and is skimmed off. The grit is collected and disposed in landfill The raw sludge: Old way: incinerated, disposed in landfill or dumped at sea New way: composted to produce a nutrient rich bacteria free material for use as fertilizerPrimary water treatment (Continued) • Ca(OH)2 and Al2 (SO4 )3 are often added to speed up the sedimentation process. 3 Ca(OH)2 + Al2(SO4)3 → 2 Al(OH)3 + 3 CaSO4 Al(OH)3 is a gelatinous precipitation that settles out slowly, carrying suspended material and bacteria with it. • Oily material floats to the surface and is skimmed off. • The grit is collected and disposed in landfill. • The raw sludge: – Old way: incinerated, disposed in landfill or dumped at sea. – New way: composted to produce a nutrient rich bacteria￾free material for use as fertilizer