May 8, 2013, 4:07 a.m.

SydneyWater has rejected suggestions untreated sewage is being discharged onto Illawarra beaches during wet weather events.

During heavy rain, the region's stormwater and wastewater goes through a treatment process involving de-gritting, screening, disinfecting and dechlorination, to remove solids and kill bacteria.

But because of the excessive flows, about 5-10 per cent bypasses the later stages of treatment, including biological processes where bacteria is used to "feed" on the organic material.

MORE: Calls for answers on sewage discharge

Wollongong Water Recycling Plant manager Stewart Ramsay said the partly treated flows had the appearance of drinking water, were heavily diluted by rainfall, and met the requirements of the plant's Environment Protection Authority licence.

The process was described as a "bypass" in line with licensing requirements, but the term was outdated.

"The term bypass, I think it conjures up thoughts of no treatment, but it's just a terminology we use," Mr Ramsay said. "Unfortunately we're stuck with that term."

Treatment processes in the Illawarra came under scrutiny during heavy rain last month when Sydney Water announced a bypass at Bombo Wastewater Treatment Plant.

The government's Beachwatch monitoring service advised swimmers to avoid Bombo and Kiama beaches for the following 24 hours due to pollution.

Original post:

Illawarra beaches free of sewage: water plant