The Port River: Adelaide's largest sewer?

Wednesday, September 7, 1994 - 10:00

By Amelia McFarlane

Question: Where can the highest concentration of red algae in the world be found? Answer: the Port Adelaide River.

This algae is a natural part of the ecosystem of the river. However, pollution levels have caused it to advance from its harmless "cyst stage" and emerge as a toxic and environmentally damaging micro-organism.

The main source of the pollution is the Port Adelaide sewage works. Each day it pumps an average of 37 million litres of effluent directly into the river. About 13.5 billion litres of effluent enter the Port River system annually.

At almost the same point as the effluent is introduced to the river, so too are 70 million litres of sea water from the nearby West Lakes. Because the effluent is less dense than the sea water, it tends to float near to, or on top of, the salty water. This causes an imbalance in the convection currents of the river, and slowly the lower layers of the river heat up.

The effluent is the main contributor to the algae problem. It contains large amounts of chemical waste, which encourages algae growth. When the waste is combined with warmer water temperatures, particularly during late spring and summer, the algae grows beyond its natural levels to produce the characteristically red algal blooms.

The predominant type of algae in the "red tide," as it is known, is Alexandrium. This algae is extremely toxic, containing a neurotoxin which can affect the human nervous system and which has caused many deaths around the world. Alexandrium thrives on the high levels of nitrogen and phosphorus in the river.

Poisoning can occur by swallowing water in which the algae's concentrations are high, eating a fish that has absorbed the algae or eating shellfish during the time of the "red tide". Shellfish poisoning can often be fatal.

There are many reports which indicate that the algae causes an inflammation of the joints known as "poly-arthritis".

Port environment

The effects of the sewage on the surrounding environment are also very clear. It kills both plants and animals.

The local seagrass, of great importance to the ecology of the port, is being destroyed. Grey mangroves are also victims because the effluent greatly reduces the nutrients which are crucial to the trees' survival.

The loss of these plants affects the breeding cycles of the river's fish. Fish nurseries have noticed a decrease in reproduction since the levels of effluent in the river began to build up.

The Engineering and Water Supply Department has made two attempts to solve the problem.

The first attempt at controlling the algae was the use of a huge propeller, installed at a cost of over $100,000. The running costs of the propeller were estimated to be around $40,000. This attempt failed to control the problem adequately.

The second attempt has involved a process of denutrification. E&WS is attempting to lower the level of phosphorous and nitrogen in the sewage effluent. It hopes to achieve this by adding a third stage to the treatment process.

Various types of bacteria will be grown, using the nitrogen and phosphorus from the effluent. These substances will then be removed from the effluent, leaving it cleaner and less nourishing to the algae.

This is a long-term project; the results are expected to be available by early 1995.

If successful, this project would benefit the Port River. However, while the effluent continues to be pumped into the river system, the problems of disturbed convection and rising water temperatures will continue.

The simplest solution to the problem is to stop the sewage works from dumping effluent into the river. This is one of the solutions the Port Adelaide Residents Environment Protection Group (PAREPG) and the local council have suggested to the state government.

They have also suggested that the effluent be treated to reduce the amount of chemicals. Other options include closing down the sewage works and setting up a sewage treatment farm.

The main obstacle to a reform of the system is that pumping dangerous waste into a natural waterway is the easiest, cheapest and most legal way to dispose of it. Why, then, should the sewage works consider anything different?

A spokesperson from PAREPG, Tony Bazeley, told Green Left Weekly that the local community was unaware of the dangers algae posed to them and the Port River. He is also concerned that the Health Commission no longer monitors the levels of Alexandrium in the river.

Bazeley feels that the PAREPG "haven't done as much" as they should have to raise public awareness of the situation. However, a sign has been erected by the group at the effluent outlet warning of the algae.

For now, as the temperatures in the Port River remain low, so too does the population of Alexandrium and other toxic algae.

But unless the problem of effluent disposal is solved, come the warmer seasons, the "red tide" will again invade the river and the effluent will continue to poison the surrounding environment.

From GLW issue 158