Obviously, water from toilets, washing facilities, washing machines, dishwashers, etc., all needs treatment to make it environmentally safe. Not all properties are on mains sewage systems, so they will need their own private treatment systems. In an earlier blog post last year we discussed some of the different products which are available for sewage treatment, and a year ago (check out the post here) we described what the differences were in types of sewage treatment plant. Here we give a bit more detail as to what is available.


Starting with domestic drainage systems, houses in rural areas will often need their own sewage treatment plants, and the old type septic tanks can generally no longer be used for new installations, although there are a few exceptions, by permit. Environmental legislation now requires high quality treatment so that the treated effluent can safely be discharged to the ground or watercourses.

Tanks-UK supply the Harlequin HydroClear (HC) and CAP ranges which are both suitable for domestic installations

The smaller sizes will be sufficient for most individual dwellings as they cover three categories: 1-6 people; 7-9 people and 10-12 people. So what’s the difference between the two ranges?


The CAP6, CAP9 and CAP12 treatment plants are continuous aeration plants, hence the name. These have an air blower which is situated at ground level in a special weatherproof housing. It is very quiet, and the sealed system means that there is no smell from it. These are really state-of-the-art treatment plants, highly efficient and low maintenance – they only need de-sludging once a year.  All of the CAP range treatment plants have a 96% overall pollutant removal level, achieved by biological treatment, which means that the resulting treated effluent is permitted to be discharged into the ground.

Looking at the HC range, these are primarily designed for larger installations, but they are also available in the smaller sizes, of HC6, HC9 and HC12, which are single tank installations suitable for single dwellings. They are more efficient (therefore higher priced) and larger than the CAP range. For instance, the HC6 has a 97% pollutant removal level, compared to 96% for the equivalent CAP6. This means it is more suitable where the discharge needs to drain straight into a ditch or waterway.  Because the chamber sizes are bigger they can cope with higher peaks of use as well.

In our blog post of February 2022, we described in detail how these systems work.

Here is a comparison chart of overall capacity and pollutant removal:

Tank capacity – Primary settlement chamber 1200 litres 1315 litres 1800 litres 2295 litres 2295 litres 2510 litres
Aeration chamber 600 litres 790 litres 900 litres 1245 litres 1245 litres 1685 litres
Final settlement 600 litres 600 litres 900 litres 935 litres 935 litres 2040 litres
Pollutant removal 96.2% 97.5% 96.2% 97.5% 96.2% 97%

Give us a call if you need help in deciding which range suits your application best.


Of course, just as there are houses off the mains drainage, there are also commercial and industrial premises which don’t have mains drainage.  And what about hotels, campsites, leisure parks and public toilets in remote areas?  These would also need a sewage treatment system, and this is where the larger sizes of HydroClear sewage treatment plants would come into their own. HC20, HC30 and HC40 have two joined tanks per system, whilst the HC50 has three. As you would imagine, HC50 is suitable for up to 50 people, so would be the ideal system for larger sites and commercial properties.

The CAP range has recently been extended to cope with medium sized commercial installations, with CAP15 and CAP18 sizes now available, still in the more compact format than the HC range.

Pump Stations

It maybe that there is not a need for a complete treatment system, if there is mains drainage situated close by. In this case you would probably use a pump station.  They provide an interim storage tank and integral pumps to transfer the effluent direct to the mains drainage where gravity alone would not work. This might be the case where a property is down a hillside from the road, for instance, or on a level but too far away to obtain the required outflow drainage fall.

For domestic installations, Harlequin have the answer with pump stations in various sizes from 450 litres up to 3200 litres.

There is another range available for larger installations, and this is the SPEL range, which are based on GRP underground tanks for extra longevity. They are available as pump station ‘packages’ which are already fitted with the required integral pumps. The horizontal tanks go right up to 300,000 litre capacity, fully kitted out as pump stations.

Just give us a call on 01953 665940 or email info@tanks-uk.com with your requirements and we’ll send you a quote.

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