The paper presents and compares the marine and atmospheric discharges
of typical large MSF and RO plants. Distillation plants require an inl
et seawater flow around 8 to 10 times the fresh water production rate,
for, cooling and feed make-up. The discharge is raised in salinity an
d in temperature, due to heat rejection from the process. A seawater R
O plant generally requires a lower feedwater flow rate of around 2.5 t
o 3 times the production. Salinity of the discharge is correspondingly
greater than in distillation, but temperature rise is small. Chemical
discharges are compared for the different processes. A comparison is
made of atmospheric emissions from generating the power to drive RO pr
ocess pumps and the emissions resulting from generation of steam and a
uxiliary power for distillation (in dual purpose desalination/power pl
ants). The factors affecting site selection and requirements for seawa
ter intakes and outfalls are briefly discussed, with examples. The lan
d area needed for a desalination plant is compared with the catchment
and reservoir areas needed for a typical surface water collection sche
me to illustrate the much lower impact of desalination on land resourc
es. Factors such as noise and aesthetics are also briefly discussed.