Eutrophication - Remediation

1. Eutrophication - Remediation Eutrophication in the Sea of Azov. Source: SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAG Developed by Richard Sandford with contributions from Martin Bloxham and Paul Worsfold,

2. Eutrophication - Remediation 5.1 Reduction in the use of phosphates as builders in detergents Polyphosphates, primarily sodium tripolyphosphate (STPP) are used in detergent formulations for washing powders and other cleaning products as “builder” compounds that stop the re- deposition of dirt. Phosphates also act to reduce the hardness of water and improve the efficiency of the detergent. Between 1950 and 1975 there was a 100% increase in the use of phosphates in detergents. The resultant accumulation of phosphates in sediments in aquatic systems is a primary cause of eutrophication.· In order to reduce the phosphate content of municipal sewage, voluntary and statutory restrictions have been introduced to limit the use of the detergent builders such as sodium tripolyphosphate. Since the middle of the 1980s the phosphorus load has been reduced by up to 50% in some European countries due to improved sewage treatment and phosphate-free detergents. A recent report on eutrophication in Europe’s coastal waters indicated that there had been a 37% reduction in the phosphate load from the UK and Ireland to the Irish Sea between 1991 and 1996. There is also evidence of significant decreasing trends in phosphorous concentrations in other European seas in the 1990s, including Danish coastal waters, the German Bight and the Wadden Sea. In Danish waters this decrease was due to an 80% reduction in the load from sewage, industry and detergents (OSPAR, 2000). Phosphate levels in the Irish Sea (1990-2000)

3. Eutrophication - Remediation 5.2 Reduction in the use of nitrate containing fertilisers Nutrients such as nitrogen and phosphorus are removed from soils by plant growth and need to be replaced. Nitrogen from mineral fertiliser is a major source of N input although inputs from animal manure remain important, especially in regions of high livestock density. Excessive nitrogen surpluses, the difference between inputs and removals by crops, can pose a threat to the environment, leading to pollution of water, air and soil. Losses to the environment can be minimised if a reasoned fertilisation is used, together with sustainable agricultural practices, such as crop rotation, planting cover crops, and ploughing in crop residues. Reasoned fertilisation means applying fertilisers, whether mineral or organic, in the correct weather conditions, (to avoid run off) at the appropriate stage in crop growth (so that plants take up the nitrogen quickly) and at the correct doses. Sources of nitrogen inputs to agriculture, 1995

4. Eutrophication - Remediation 5.3 Implementation of tertiary sewage treatment methods which remove phosphate and nitrate The treatment of sewage involves three main phases that are usually referred to as primary, secondary and tertiary treatment. Primary treatment involves the removal of debris such as rags, wood and grit, secondary treatment involves the reduction of the amount of organic matter in the water and tertiary treatment involves the removal of other undesirable species such as nitrate and/or phosphate ions. In 1991, the EU Urban Waste Water Directive came into force requiring all significant discharges (over 15,000 population equivalent) to have a minimum of secondary treatment by 2000. Figures collected by Water UK show that for 1997/98, of a total population equivalent of about 9.5 million connected to sewage treatment works discharging to sea outfalls, 26% received no or preliminary treatment, 66% received primary or secondary treatment and 8% received tertiary treatment. Primary treatment is carried out by the removal of gross debris using metal screens, bars or choppers, removal of silt and grit using a grit chamber, and the removal of suspended matter by sedimentation. Secondary treatment is designed to reduce the level of organic material in the water. Typically, 90% of the BOD (Biological Oxygen Demand) is removed during process using either trickle filtration or the activated sludge process. Tertiary treatment is designed to remove any undesirable species from the water prior to discharge into a river. Tertiary treatment typically involves removal of phosphate by chemical precipitation and nitrate by denitrification.

5. Eutrophication - Remediation Nutrient levels in the Irish Sea Trend analysis based on nutrient-salinity regressions indicate that there has been a decrease in orthophosphate levels in the near surface waters of the south west Irish Sea (39%) and north west Irish Sea (33%) over the last decade with no change in the mid Irish Sea. TON levels have remained constant in the south west and north west Irish Sea but have increased in the mid Irish Sea. However, over the last 4 years, nutrient-salinity regressions indicate that there is evidence of a significant decrease in TON levels in the north west, mid and south west Irish Sea with no apparent trends in phosphate levels. The decrease in orthophosphate concentrations between 1990 and 2000 may have been a result of a reduction in the load from sewage, industry and detergents. Source: Bloxham, M., et al., Winter Nutrient Monitoring of the Western Irish Sea- 1990-2000, Irish Marine Environment and Health Series, 2001. Trend analysis of orthophosphate in the north west Irish Sea (1991-1999)

6. Eutrophication - Remediation Sources of nitrogen inputs to agriculture from EU countries in 1995 (Source: Eurostat) Note: Nitrogen input from other sources include: nitrogen from biological fixation and atmospheric deposition

7. Raw sewage To water body Primary Treatment Secondary Treatment Tertiary Treatment To remove debris and sediment To remove organic matter To remove NO3- or PO43- Eutrophication - Remediation Three main phases of sewage treatment

8. Eutrophication - Remediation Tertiary sewage treatment Chemical precipitation is commonly used to remove phosphate ions: Al3+(aq) + PO43-(aq) AlPO4(s) Fe3+(aq) + PO43-(aq) FePO4(s) Denitrification makes use of a specialised group of bacteria that live under anaerobic conditions and use nitrate ions as a means of oxidising carbohydrates to produce energy: Denitrifying Bacteria [CH2O] and NO3- CO2 and H2O and N2 or N2O In the process the nitrate ions (NO3-) are reduced to nitrogen (N2) or dinitrogen oxide (N2O).