Why rainwater is overwhelming our sewerage system

All over Wales sewers are struggling. The main problem is too much liquid, with run off rain water from our roofs, roads and other hard surfaces overwhelming the system. The result is raw sewage discharged to rivers and sea, or (rarely but increasingly) backing up in homes or welling out of manholes.

In my county of Pembrokeshire a meeting between Dŵr Cymru and the Council in 2009 was a litany of sewer failure and leaks reported from 21 places. There were also complaints included that housing could not be built due to sewer incapacity. In only one place, Haverfordwest, was sustainable urban drainage being considered. This would divert rainwater from sewers and duct it into pools and rivers where it would have ended up in the first place, had we not got in the way with our hard surfaces and sewers.

Less obvious but more threatening is nutrient loss. There are now so many people consuming the earth’s mineral nutrients in food, that we cannot afford to loose them to the sea. For example, the world supply of phosphorus for phosphates is limited and contained in very few countries. At current usage we have only have enough for a few decades, while the USA is running out now.

Phosphates run out through sewers and into rivers and the sea which become polluted and die. It is a macro nutrient, the P in NPK, the fertiliser behind our food behind our population levels. The feverish price spikes which precede real scarcity have begun. Between 2007 and 2009 the phosphates price quadrupled. China placed a strong export tariff on phosphates, in effect hoarding it. However, this year the price has fallen back.

At a recent seminar on the issue, held at the West Wales Eco Centre in Newport,  Simon Broom, Dŵr Cymru design manager, grabbed a bit of paper and  drew the rise of rain water, similar to the global warming curve. He explained the rise was due to a combination of increased impermeable surfaces as people tarmac their front gardens, expanding towns, roads and car parks, and to climate change itself. The trend is for more intense heavy bursts of rain, perfect for flooding and sewer overload.

The first line he drew disappeared skyward. He drew a second shaped like a mountain. This, he explained, was ground water entering sewers. Dŵr Cymru’s stronger policy and new investment would slow down the disastrous increase. In ten years it would be heading downhill to arrive back at today’s level, which he admitted was still too high, in about thirty years. Only then would an actual reduction begin.

Simon Broom acknowledged that not enough had been done in the past, but said sustainability is now the name of the game. Dŵr Cymru has its engine revving, and is shovelling in enthusiasm and money to reach it’s golden shores. Along with other Welsh organisations such as the Environment Agency, it sees itself as taking a leading role in addressing a UK-wide problem. As he put it, “We are the only water board in the British Isles to invest £22 million from OFWAT to get surface water out of sewers”.

Sewage contains invaluable nutrients. Meanwhile the surface water we currently waste by allowing it to run through the sewage system could be used instead for multiple purposes, from irrigation for food production, to washing cars. Separating surface water from sewage would save money in pumping, treatment, and infrastructure, and keep at bay that dreaded sight, the lifting manhole cover.

The present solution to sewer treatment overload is combined sewer overflow. These are pipes discharging untreated dilute sewage into rivers or the sea. They are meant for emergency use only, under licence from the Environment Agency. However, they have crept into routine use in many places, causing loss of some beach blue flag status and EU dismay at pollution of our rivers. In the past monitoring of discharge was farmed out by Dŵr Cymru to private contractors, Latterly cost savings have result in cutbacks to this monitoring, resulting  in a black hole in the data on combined sewer overflow discharges.

When the rain finally stopped last summer in Newport and the tourists rushed into the sea, two families chatting afterwards found they had both contacted violent gastro intestinal infections after swallowing sea-water. They made investigations and were shocked at the possible cause.

I have been in meetings where town councils decide to hush the matter up. After all it isn’t proven, the tourists mustn’t be frightened off. It’s their health or our money… shh!

But there are financial impacts, too. The most tragic was the mass die-off of cockles in the Bury inlet on the Gower. This Welsh cockle fishery was the fifth in the world to get the prized marine stewardship council accreditation for sustainable fishing, and is still the only one in Wales fully accredited.  However, the cockles bred at an unnatural rate and then died prematurely. The last bed to die off was the least nutrient rich. The symptoms implicated the combined sewer overflow, which fishermen blamed for their lost livelihood. Dŵr Cymru correctly responds that this is not proven as the cause, which remains mysterious. They are not guilty until proven, which is lucky as there would be compensation issues.

Nonetheless, Dŵr Cymru is acting to stop ground water entering the Llanelli and Gower sewers so the solids can be treated and used on land. Nine small diversions have been completed, reducing the flow by 30 litres a second. There are 61 more diversions to divert, and huge ingress from joint leaks, cracks and porosity in the Victorian pipe work.

Separating ground water is the biggest challenge facing our sewerage system, but it is not the most sexy. Much bigger money, £70 million,  is going on three Advanced Digesters for Wales. These massive beasts heat sewage sludge and extract methane through anaerobic digestion. The gas generates electricity. The heat by-product of generation accelerates the digestion process. Surplus electricity goes to the grid.

Methane comes from sewage naturally but the advanced version gets more out much faster. Once de-watered the residue is a light, crumbly, odourless fertiliser. “It will be virtually given away to farmers,” Andrew Bowen, South West Wales waste water manager confided. “Our digester in Cardiff will be the biggest so far in Britain, coming on stream in December and fully commissioned next year.”

I asked about the possibility of smaller-scale methane digesters as used on modest sized farms throughout the continent. Efficiency and return on investment, was the justification for the giantist approach. It does mean trucking sludge great distances, as quantities are essential for their operation. For this and other reasons I suspect smaller dispersed processing is the future, matching the nutrients to the area needing them.

At home we have a series of reed beds to treat seven households’ liquid effluent, polluting bulk output of sewage. Reed beds are elegant and odourless. They are engineered using graded stones over a membrane providing aerated surfaces for digestion. The reeds grow tall on the nutrients, while a self-powered doser ensures spread of the fluids. You can live right next to this garden amenity and enjoy the reed birds and insects with only the faintest occasional whiff. Dŵr Cymru uses reed beds to treat small hamlets. Their engineers showed me the testing equipment at the outfall, demonstrating a 90 per cent cleansing rate. “You could drink it”, they claimed without offering to demonstrate. “It achieves better results than UV light treatment, and we only need to weed and cut the reeds once a year”. However, reed beds are generally limited by land availability.

Yesterday’s technological triumph of UV light treatment, which breaks up the DNA of the bacteria, is now turned off in winter to save the exorbitant costs. Surfers who ride in the stormy winter fear disease. The seriousness of this issue is not contested by the trade. The Chartered Institute of Water Management summarises the dilemma as follows:

“Despite the considerable dilution by surface water runoff, storm sewage discharges from combined sewer overflows may contain significant loads of a wide variety of pollutants, including bacteria and viruses, oxygen demanding and toxic pollutants, as well as persistent materials such as heavy metals, Polycyclic Aromatic Hydrocarbons, etc. The presence of gross solids of obvious sewage origin is also a frequent problem. Although only discharged over short periods of time on an infrequent basis, these pollutants can seriously compromise many beneficial uses of receiving waters such as fisheries, shellfisheries, bathing and recreational water use. In extreme cases, combined sewer overflow discharges can result in fish mortalities, shellfish unfit for human consumption, public health hazards and visual and odour problems. The cost of upsizing combined sewer systems and treatment facilities to accommodate all flows is prohibitive, as is the cost of universal separation of all existing combined sewers systems.”

Dŵr Cymru has a surface water strategy aiming to:

“Return all surface water to the ground or open water as quickly as possible… We are a large energy user and we want to reduce our carbon footprint… Reducing surface run-off will produce a dual benefit by protecting local environments and reducing carbon emissions.”

Should we be regarding costs as prohibitive?  We can’t stop the rain, we can’t stop the sewerage, but costs are a matter of our priorities. Combining ground water and sewage and dumping it at sea means endless waste and expense. Separating them ends waste and restores invaluable resources to productive use. Roofs have downspouts, roads have drains, and we have systems for kerbside rainwater collection. All we need is conduits next time the road comes up for repair. Or streams for children’s rainy day sploshing.