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Scotland's Marine Atlas: Information for The National Marine Plan

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WASTE DISPOSAL (WASTE WATER TREATMENT AND INDUSTRIAL OUTFALLS)

What, why and where?

Waste water treatment is designed to process waste water whilst protecting the environment and maintaining public health. Outfalls to the marine environment fall into three categories. Outfalls from waste water treatment ( WWT) plants which process waste water from the mains sewerage system; industrial sites which take waste from manufacturing plants; and some private domestic sources. These categories of outfall also discharge to the riverine freshwater environment which eventually reach the sea.

All sewerage systems that also collect rainwater (combined sewers) need overflow outlets (combined sewer overflows) that deal with the extra water collected during some rainstorms. Without these safety valves there would be a flooding risk at both the sewerage works and in other properties. Sewage in these overflow discharges is diluted with significant amounts of rainwater.

Treatment

There are four types of treatment undertaken at waste water treatment plants:

Preliminary treatment is the first stage of the process and involves the removal of coarse solids and large materials.

Primary treatment is a physical and/or chemical process involving settlement of suspended solids.

Secondary treatment is a process generally involving biological treatment either with secondary settlement or another process. Secondary treatment is designed to reduce the suspended solids and oxygen demand. It also reduces the bacterial content of sewage.

Tertiary treatment is the final stage of the process and can include filtration, removal of nutrients such as phosphorous and nitrogen, and disinfection, for example by UV light.

The Urban Waste Water Treatment Directive 1991 sets out treatment levels for waste water based on the population equivalent of the plant catchment and the sensitivity of the water receiving the discharges.

WWT plants and outfalls are found all around the coastline near villages, towns and cities. Those with the larger capacity and higher treatment levels being concentrated in the major firths, near large cities or near sensitive receiving waters.

Scottish Water provides sewerage services to the majority of households in Scotland, although some households have private discharges. Data on private discharges such as septic tanks are not included in this Atlas.

Industrial effluent discharges are licensed if the volume of effluent is >10m 3/day and has a population equivalent >15 and are subject to control placed on the amount and nature of the discharge. SEPA regulates such outfall discharges through The Water Environment (Controlled Activities) (Scotland) Regulations 2005 ( CAR Regulations).

Details of substances recorded in the seas, from both waste water and industrial outfalls are in Chapter 3.

Numbers of outfalls discharging at the coast

Sea area

No. of industrial outfalls

No. of WWT outfalls

Total

Solway Firth, North Channel

8

24

32

Clyde

26

61

87

Minches and Malin Sea

12

86

98

Hebrides

25

25

North Scotland Coast

4

26

30

West Shetland

2

33

35

East Shetland

6

37

43

Moray Firth

9

39

48

East Scotland Coast

16

20

36

Forth

29

33

62

Total

112

384

496

Source: SEPASPRI database (1)

Types of treatment per sea area for waste water treatment

Sea area

Total WWT outfalls

preliminary

primary

secondary

tertiary

Solway Firth, North Channel

24

1

15

8

Clyde

61

2

44

15

Minches and Malin Sea

86

72

13

1

Hebrides

25

23

2

North Scotland Coast

26

21

5

West Shetland

33

33

East Shetland

37

36

1

Moray Firth

39

2

14

15

8

East Scotland Coast

20

3

3

12

2

Forth

33

5

9

16

3

Totals

384

13

270

87

14

Source: SEPA

Volumes of outfalls per sea area for waste water treatment

Sea area

Total WWT outfalls

Volumes per day

0 to
5m 3

> 5 to
20m 3

> 20 to
100m 3

> 100 to
1000m
3

> 1,000 to
10,000m
3

> 10,000 to
50,000m
3

> 50,000 to
150,000m
3

> 150,000m 3

Solway Firth, North Channel

24

2

11

8

3

Clyde

61

9

16

21

6

5

1

3

Minches and Malin Sea

86

2

8

44

24

7

1

Hebrides

25

1

2

15

7

North Scotland Coast

26

1

3

9

11

2

West Shetland

33

1

15

13

4

East Shetland

37

3

9

21

3

1

Moray Firth

39

1

7

10

14

6

1

East Scotland Coast

20

2

7

4

5

2

Forth

33

4

17

6

4

2

Totals

384

8

47

129

102

57

28

6

7

Source: SEPA

Locations and treatment types of waste water treatment plants

Locations and treatment types of waste water treatment plants

Contribution to the economy

The disposal of waste water at sea is an ecosystem service, creating the benefit of costs saved compared to alternative means of disposal. The value of this benefit cannot be calculated with certainty. In economic terms, waste water treatment and industrial outfalls do not generate a measurable output and their contribution can therefore not be measured, from ABI data, in terms of GVA or employee jobs provided.

It has been estimated that £5.83M of SEPA's income is generated by licences issued for disposal in coastal waters (2). Between 2003/04 and 2008/09, Scottish Water invested £292M in activity, including new waste water treatment plants, to comply with the Urban Waste Water Treatment Directive requirement for all urban areas to have appropriate waste water treatment collection systems by 2005. During the same period a further £41M was invested to improve treatment facilities to meet the requirements of the Bathing Waters Directive.

Pressures and impacts on Scotland's socio-economics

Positive

  • Allows industries to function by providing a service
  • Employment
  • Provides clean seas for other activities e.g. bathing, aquaculture, public health
  • Reduces risk of flooding
  • Provision of infrastructure for waste water collection

Negative

  • Potential pollution especially if systems fail
  • Possible obstruction on seabed
  • Local nutrient enrichment affecting fisheries and other uses of coastal waters
  • Release of pathogens including some that can have adverse health consequences for marine wildlife and for human health.

Source: Based on CP2 PSEG Feeder Report section 3.16.6 (2) and UK Marine Policy Statement (3)

Pressures and impacts on theenvironment

Pressure theme: Pollution and other chemical pressures
Pressure: Hazardous substances
Impact: Risk of pollution, reduced water and sediment quality. Possible mortality of organisms from organic, metal and radioactive contaminants, from industrial discharges.

Pressure: Addition of nutrients e.g. nitrogen, phosphates and derivatives
Impact: Risk of eutrophication, potentially resulting in changes in the species composition of phytoplankton communities, toxin producing and harmful algal blooms. Possible loss of submerged vegetation through shading, development of hypoxic conditions due to decomposition of excess plant biomass, changes in benthic community structure due to hypoxia or toxic algae, fatalities of fauna due to oxygen deficiencies.

Pressure: Addition of organic matter
Impact:
Removal of oxygen from the water column and deposition of organic matter on the seabed leading to fatalities of fauna due to oxygen deficiencies and changes in benthic community structure.

Pressure theme: Other physical pressures
Pressure: Litter in wastewater
Impact: Risk of harm to wildlife through ingestion or entanglement.

Pressure theme: Biological pressures
Pressure: Addition of faecal material
Impact: Pathogens (bacteria, viruses or parasites) may cause illness/infection if ingested through recreational water use or shellfish consumption.

Source: CP2 PSEG Feeder Report table 3.112 (2)

Chapter 3 reports on the impacts of the discharges on the marine environment.

Lerwick waste water treatment plant (Shetland)

Lerwick waste water treatment plant (Shetland)
© Scottish Water

Forward look

Scottish Water has been set objectives for 2010-2015. Relevant to the marine environment these include improving the quality of wastewater treatment works discharges to ensure compliance with the environmental standards set out in all appropriate directives. There is also a requirement to plan for the provision of new strategic capacity to meet the needs of all new housing development until 2020. Work is ongoing to identify what this means for new treatment works and outfalls at the coast. However, there are requirements in various directives to ensure minimal impact and a sustainable co-existence with other existing marine activities such as aquaculture, fishing and bathing.

Seafield, Edinburgh waste water treatment works

Seafield, Edinburgh waste water treatment works
© Aerial Photography Solutions

Locations and types of industrial marine discharges

Locations and types of industrial marine discharges