Package Sewage & Effluent Treatment Plants: Problems with Specification, Design, Installation, Commissioning and Troubleshooting


Our principal consultant, Sean Moran is a Chartered Engineer with many years of experience as a process trouble-shooter, and has substantial experience of resolving problems with packaged sewage treatment plants from single dwelling to a few hundred population equivalent sizes. These have mainly been submerged aerated filter systems, or sequencing batch reactors, although Sean is familiar with all sewage and water treatment technologies.

Sean has never been faced with a problem for which he could not find a technical solution, despite often having been preceded to site by many other supposed trouble-shooters. If you have a problem which has resisted all attempts to fix it, we'd love to hear from you. There's nothing Sean likes better than a challenge.

Whilst Sean has been able to advise clients on how to solve their process problems in all cases, it would have been much cheaper for these clients if they had engaged a professional engineer sooner, rather than later.

Examples from Previous Projects

a. Training Centre

A package plant which was supposed to aerate sewage from a training centre was buried underground in an airtight chamber. Naturally it never worked, and smelled bad whenever the covers were opened. The corrosive gases produced dissolved the badly specified concrete of the chamber, which fell into the aeration tank. Three years of visits from plant installers failed to notice that air conduits supposed to carry air into system had not been fitted. When they were eventually asked at our request to fit the conduits, they fitted them to the primary tank, instead of the treatment chamber. The "designer" was forced to upgrade the plant in accordance with our recommendations at their own expense, as the client still had retention monies. Before our visit the "designer" insisted the plant worked, despite no valid sample evidence.

A package plant which was supposed to aerate sewage from a training centre was buried underground in an airtight chamber

Photo shows a package plant buried underground in an airtight chamber. Note very poor installation quality: Package plant installers are not professional engineers 
The corrosive gases produced by the above installation dissolved the badly specified concrete of the chamber, which fell into the aeration tank

Photo shows how the corrosive gases produced had dissolved the badly specified concrete of the chamber, which fell into the aeration tank.


Three years of visits from plant installers had failed to notice that the air conduits supposed to carry air into system had not been fitted.

Photo shows failure to fit air conduits supposed to carry air into system. The vent in the left of this shot is not connected to the surface.

When the installers were eventually told at my request to fit the conduits, they fitted them to the primary tank, instead of the treatment chamber.

Photo shows conduits fitted to the primary tank instead of the treatment chamber

b. New Housing Development

Several package plants which were supposed to treat effluent from small housing developments, usually including ammonia removal. Several years after installation, after the original installers had failed to make the plant work, we were called in to see if the plant was working. The plant was found never to have worked, having been radically undersized by incompetent "designers". The plants were too small ever to work, and are now being replaced, repaired or upgraded at the designers' expense, as the works were covered under NHBC guarantee. Before our visits, the "designer" insisted the plant worked, despite there never having been a passing sample. This is a fairly common occurrence, and we have been called out to several plants answering to the previous description.

c. Country Hotel

A package plant which had created odour nuisance for years at a country hotel was found to have been fitted with feed pumps which fed the plant at twenty times its maximum rated flow by unqualified "drainage engineers". This plant has also never worked, but the suppliers had sold the client irrelevant or positively detrimental bolt-on extra products over and over again, none of which addressed the basic problem. After five years of this we were called in. The plant is now being modified to bring incoming flow within the package designers' allowable flow rates, which has solved the odour problem. The "drainage engineers" still do not understand that the plant did not work, let alone why.

d. Private Country House

A package plant at a large country house which was in perfect working order was scrapped on the advice of someone calling themselves a "consulting engineer" despite having no degree in any subject, or even any tradesman's qualifications. Our client was asked to pay for the replacement plant, which had been so oversized in an attempt to cover up for the lack of knowledge of the so called engineer, that it would not work. The purchaser of the plant had wasted a great deal of money, as the so called engineer did not understand that the root of the problem was not simple overloading, but lack of control of effluent arising from a new laundry discharging to the plant. Our client has been advised to install their own small plant much more cheaply than becoming involved in the problematic installation.

e. Restaurants (x2)

New package plants were installed without being encased in concrete as per manufacturers specification in areas with high groundwater levels, and were therefore crushed. One was fed by a home-made grease trap constructed by a local farmer and designed by no-one. The same farmer had also advised the client to use the working package plant on site as a simple holding tank. The consequence of this catalogue of errors is that it was cheaper to install a pumped main to the nearest sewer a mile away than fix what had been done to the plant. Another had no grease trap despite clear requirement from the Environment Agency to install one, and staff routinely pouring hot grease directly into the line going into the plant.

f. Commercial facilities (x3)

We have seen a number of massively oversized Submerged Aerated Filter (SAF) plants recently at commercial premises, where owners had thought that their plants were undersized by virtue of their consitent failure to meet consent. Plants may be oversized as well as undersized if professional engineers are not involved in system design. Both of these plants also had undersized settlement tanks. Both are now making modifications suggested by Expertise Limited to their plants to solve their design problems.

General Advice to Owners and Designers

Most of the companies installing such systems have no staff with relevant formal qualifications or any knowledge whatever of how to design such a system. They purchase these systems from manufacturers who sell them as products without guarantee, expecting them to be sold by or to professional engineers who can satisfy themselves as to their suitability. The companies selling these products often no longer employ the engineer who designed their product, and their representatives are not qualified process engineers. In any case, they are salesmen, not consultants. These manufacturers make clear in their quotations that no guarantees are offered, and all is at the client's risk, but all too often clients think they have covered themselves when in fact no one who understands these systems has looked at risk to the client. In our experience, the companies offering these packaged systems act in good faith. We have experience of Clearwater, Conder, WPL, Titan / Entec, Biotank and many other manufacturers' plants. In every case, the package plant vendor made clear in their quotation that no guarantees were offered, and the clients' representatives (usually architects) failed to notice that they were buying a big green box with no guarantee of anything with respect to performance. In most cases, installers of these systems do not understand how to properly specify, install, or maintain the systems, and are at a loss when it comes to a plant which is not working properly. They do no valid tests to prove that the plant works before they leave site. They do not train the client or their staff. They are usually however the last to admit this. Most of the plants we have visited recently have actually never worked, and a high proportion of them can not be made to work without radical modification, having been badly specified or installed in the first place.

A word to architects: many of the examples above were specified by architects, in collaboration with package plant installers. Package plant installers are not professional engineers, and one should note that quotations from package plant suppliers almost always specifically avoid offering process guarantees. Most of the previous examples cost architects in money and more importantly in reputation. Consult a professional engineer who is not trying to sell equipment when specifying this sort of machinery: it will save money. Installers might describe themselves as drainage engineers, or even consulting engineers, but prospective clients should ask them who is designing their system. Why not ask them if their Professional Liability Insurance covers them for design of process plant? Insurance companies are shrewd judges of a company's abilities. A wise client will ask to see that a Chartered Chemical Engineer has oversight of the design specification, and that valid performance tests and process guarantees are offered. No number of years of experience of selling non-guaranteed packages designed by a third party gives the ability to properly specify, design, install, commission, or troubleshoot these plants. This does not stop any number of companies from attempting to do so. Often they get lucky, but it can be an expensive gamble for clients who find out that with no guarantees, they are the losers when the plant does not work.