Marine Plant Systems Pty Ltd

Sales, After Sales, Service

Sewage Sludge: The Second Waste Stream


Modern sewage treatment plants have two waste streams. The primary waste stream is treated sewage. This is the effluent stream that is safe for discharge according to IMO regulations. The second waste stream is sludge. Every machine that cleans sewage retains sludge. It's important to know how much sludge is expected and how it is controlled in the sewage treatment plant you are considering for your project.

Most of you are familiar with oily water separators. The separator takes water from the bilge of a ship, separates out the oil and discharges the clean water overboard in accordance with the rules of IMO. The oil residue is transferred to a oil sludge tank.

Modern sewage treatment plants operate on a similar basis. Sewage is pumped through the sewage treatment plant where the solid human intestinal torpedoes (hereinafter called s.h.i.t) are partially scrubbed out of the water. Type approved testing requires at least 500mg/l solids goes into the sewage treatment plant. The sewage treatment plant has to scrub a fair amount of shit out of the water because no more than 35mg/l solids is permissible in the discharge of the sewage treatment plant. That’s a 93% reduction. Thus, 500-35=465mg/l. So where does 465mg/l get retained? Remember that this is shit. If shit disappeared into thin air, we wouldn't need sewage treatment plants. Those residual solids, much like the residual oil from our oily water separators, must be retained somewhere. That's the whole purpose of treating sewage: clean the water so it's less harmful to the marine environment.

Some makers use filters. That's right: shit filters. I would not want to be the engineer who has to isolate, dismount and clean or replace that filter. How will you store used filters caked with decomposing shit?

Some makers allow the sludge to settle out inside their sewage treatment plant. That's fine for a short amount of time however once the shit piles up, someone is going to have to clean it out.

Some makers allow the shit to pile up inside the sewage treatment plant then discharge it back into the ship's sewage collection tank. This seems a bit retarded considering that crew are trying to keep the tanks clean and that the sludge will effectively increase the solids load going right back into the sewage treatment plant. Does an oily water separator discharge the oil sludge back into the bilge? NO. The consequence: the influent quality will deteriorate as the solids and organic load rise beyond the capability of the sewage treatment plant.

Finally, other makers use filters and membranes. The discharged water from these plants is very clean however the sensitivity of these systems is normally beyond the acceptable tolerances of a ship. No one wants to babysit the sewage treatment plant, replace the shit filters, back flush or replace membranes when they get blocked or damaged due to toxic fouling.

This is why Hamann separates out 98% of the shit and drops it into a dedicated tank. This is why the Hamann sewage treatment plants self-clean. Hamann know that if you ignore your shit, it's going to pile up and become your worst nightmare. Don't invest in something that is going to make you do all the dirty work.

Please challenge anyone that tells you that their sewage treatment plant does not generate sludge as a part of the treatment process.

Remember 500-35=465mg/l. If they take shit out of the water, where does it go? If you don't check, confirm and get the maker to warrant their claim, you may end up with all that residual shit in your hands.

If you have any questions, call our office and speak to a specialist. We talk about shit all day everyday and are here to give you the benefit of our knowledge and experience. Information is free. Please take advantage of what we have learned so you can make an informed decision about the sewage treatment plant you are considering.

Hamann sludge production


2.5% of treated sewage is retained as sludge.
who we are
We are a marine equipment agency and service station for high-quality machinery manufacturers. We are staffed by marine engineers and project managers. Our products are warranted and we service what we sell.
contact us
Marine Plant Systems Pty Ltd
6/8 Redemptora Road
Henderson WA 6166
Tel. (08) 9410 0144
Fax (08) 9410 0155
sales@marineplantsystems.com
what we do
Marine equipment sales, service, commissioning assistance, warranty administration, troubleshooting, after sales, spare parts, equipment surveys, condition reports.