Final answer:
The first step in wastewater treatment is pretreatment, which includes screening and removing sand and gravel to protect the equipment and improve the efficiency of subsequent treatment processes. Option b
Step-by-step explanation:
The first step in wastewater treatment is pretreatment, which includes screening and the removal of sand and gravel. This step is essential to prevent any large debris or inorganic solids such as sand from damaging the equipment or hindering subsequent treatment processes.
After pretreatment, the wastewater undergoes primary treatment which involves the settling or floatation to remove organic solids, fats, and greases. Option b.