lakepromo hungarian seminar: 10-14th october, 2007 email: [email protected] rural wastewater...

Lakepromo Hungarian seminar: 10-14th October, 2007 Email: [email protected]

Rural wastewater treatment in the United Kingdom

Dave Diston, Huw Taylor

School of Environment and Technology,

University of Brighton


Characteristics of UK aquatic pollution

• Point/diffuse source contribution of P to surface waters is estimated to be 50:50 – N is biased towards diffuse

• Point source contribution judged to be of greater importance to riverine eutrophication (SRP; PO4)

• Government action (no specific rural sewage treatment plan):

– Adoption of numerous EU Directives (UWWTD, WFD etc);

– Agri-environmental schemes. http://www.defra.gov.uk/erdp/schemes/es/default.htm


UK water industry – Key facts- Transition from public to private (1989)- Drivers:

– Removal from government financial regulations. Newly created private companies were granted increased borrowing powers free from Treasury constraints;

– New companies were floated on the stock market, upon which previous accrued debts were written off, making shares more attractive;

– The companies were allowed to increase water and waste processing prices (subject to regulation).

Component % 1989-2006 Increase (excluding inflation)

Water 45.9

Sewage 36.7

Combined 41

Table 1: Price changes in the post-privatisation period (Ofwat)

Profit production was now of major importnace


Companies involved in water service industry

Brighton

London

98% of UK households are connected to the mains sewerage network, owned and operated by 11 private regionalwater and sewerage companies

Water and sewage Water only


Have goals of privatisation been achieved?

1980-1985 1985-1990 1990-1995 1995-2000 2000-2005 2005-2010

Water and Sewage companies

1.5bn 1.9bn 3.3bn 3.5bn 3.1bn 3.2bn

Water Only n/a n/a 0.2bn 0.3bn 0.2bn 0.2bn

Total 1.5bn 1.9bn 3.5bn 3.8bn 3.3bn 3.4bn

Table 2: Average annual capital investment

Privatisation


Current practices and methods available for the treatment of non-mains connected rural households (2%)in the UK (i)

• Cesspool (storage only, little treatment)

Pipe delivering sewage from single property (>15m)

Pebbles and rocks

Gravel

Capacity = 18 – 50 m3

Filter

After construction,an airtight lid mustbe placed overcesspool

PROS = Cheaply & quickly built; CONS = No treatment, frequent emptying (££), access required


Current practices and methods available for the treatment of non-mains connected rural households in the UK (ii)

• Septic tank (primary sedimentation and some biological treatment)

Design details can be found in British Standard BS 6297:1983

Up to 70% BODremoval

PROS = Decent treatment (30/20), de-sludging ~ 1 year, easily maintained ; CONS = Potential for bio-damage, backing up common


Two septic tanks in series for populations up to 30 persons (BS 6297:1983)

Design and capacities vary greatly depending onpopulation to beserved


Current practices and methods available for the treatment of non-mains connected rural households in the UK (iii)

• Packaged plants (sedimentation and biological treatment)

Various configurationse.g. Activated sludge/biofiltration etc.PROS = High level of treatment; CONS = Expensive (6 person = £2,000+)


Current practices and methods available for the treatment of non-mains connected rural households in the UK (iv)

• Other options:– Small STW (same in

principle to large STW – albeit on a smaller scale).

– Tertiary treatment:• Grass plots;

• Upward flow clarifiers;

• Effluent lagoons;

• Reed bed systems

Technical drawings of all systems are available upon request


Extent of methods (i)

Type Pre 1945 1945-1990 1991-2001 Mains connection 95.9% 98.9% 97.8% Septic 3.0% 0.8% 1.7% Cesspool 0.7% 0.1% 0.0% Private STW 0.3% 0.1% 0.3% Unknown 0.1% 0.1% 0.2%

Table 3: Drainage attributes in UK households by construction date Inc via private sewer

Proportions have remained relatively stable


Extent of methods by region (ii)

1 Figures are estimates and apply to septic tanks only2 Figures are estimates and apply to septic tanks and package sewage treatment works

Region % Sewered Unsewered properties (000s)

Approximate consents (1) 000s

EA estimate(2) 000s

Anglian 93 167 10 - Northumbrian 98 21 - 5 North West 98 55 1 - Severn Trent 97 100 7 70 Southern 95 90 - 30 South West 88 70 - 20 Thames 98 94 4 - Welsh 93 93 - - Wessex 93 72 - 50 Yorkshire 97 57 - 10 ENGLAND AND WALES

96 819 35 185

Table 4: Sewerage in England and Wales

No clear spatial patterns


Current practices and methods available for the treatment of mains connected rural wastewater in the UK (i)

• Different experience of rural sewage processes to other Lakepromo partners – most rural households are connected to the mains sewerage network sewage is processed in central STW

• Many rural properties are connected via Private Sewer Networks


Current practices and methods available for the treatment of mains connected rural wastewater in the UK (ii)

• Private Sewers– There are approximately 9,450,000

properties served by private sewers in the UK of which it is estimated 7,097,500 (75%) are located in rural areas

– Recent data indicated there were a total of 282,000 internal and external-flooding incidents per annum associated with all private sewers. However, Local Authorities only recorded 120,000 sewer related flooding incidents, whilst Ofwat only recorded 5,700 internal flooding incidents. Therefore, it is likely many sewer faults are not reported, limiting the chance of exercising damage mitigation strategies.

ICG % by length 1 2 3 4 5

55 12 16 15 2

Note: Internal Condition Grade (ICG) 1: Acceptable conditionICG2: Short-term risk of collapse is minimalICG3: Collapse unlikely in near future, but likely to deteriorateICG4: Collapse likely in foreseeable futureICG5: Collapse imminent/collapsed

Table 5: Condition of private sewers


Current practices and methods available for the treatment of mains connected rural wastewater in the UK (iii)

Problem Type Number of incidents per annum

Ownership disputes 45,000 Flooding due to public sewer surcharging 42,000 Flooding due to structurally defective private sewers 46,000 Flooding due to hydraulically defective private sewers 20,000 Failure of pitch fibre pipes 50,000 Lateral drains 58,000

Table 6: Reasons for private sewer faults

Total faults = 261,000


Other areas included in the UK Rural Sewage Treatment Information Package

• History of UK sewage treatment• Administrative structure and legislation• Planning and implementation procedures• Methodology for selection of appropriate system• National special expertise (reed bed systems) • Investigation into nutrient stripping within the UK


Thank you for your attention!

Questions after part II

lakepromo hungarian seminar: 10-14th october, 2007 email: [email protected] rural wastewater...

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