Organic Nutrient Pollution

PROCESSES INVOLVING ANIMAL/PLANT PRODUCTS (produce liquid effluents containing organic nutrients such as carbs, lipids and proteins) INCLUDE: - sewage works - manure disposal - silage storage - leather tanneries - paper mills - food processing plants

• deoxygenation • pathogens • inorganic nutrient release

• untreated org nutrients flowing into rivers/lakes provide food for microorgs in water • as a result, their aerobic digestion deoxygenates the water and may kill aerobic orgs like fish and insects • microorgs also cover the river/lake bed, preventing light from reaching normal water plants, inhibiting PTS, killing the plants and disrupting the food webs • eutrophication can also occur with ONP as microbial decay releases inorg nutrients

sewage can contain pathogens from infected people - if other people came into contact with these pathogens either directly or through contaminated food or water, the disease can spread e.g. cholera, typhoid, dysentry

• organic nutrients do not cause eutroph directly as they provide nutrients for heterotrophs not nutrients for photoautotrophs • however, as they decay, they may release inorganic nutrients that cause eutrophication

• used to be common to discharge sewage into rivers/sea, now illegal in many countries • prevents deoxygenation of water bodies • additional processes may be used to treat pathogens/inorganic nutrients

designed to treat the specific effluent it receives to a satisfactory standard so the fluids can be discharged without causing unacceptable pollution - the standard varies according to location: a higher standard may be required in more sensitive environments or where there are more people

WATER FROM: - toilet flushing - clothes washing - dishes - personal hygiene - road drainage water - non-toxic industrial waste Therefore the actual concentration of sewage is actually very low - (typically 250kg water containing 2-3kg liquid and solid sewage per person per day)

• pre-treatment methods: removal of solid objects like paper, plastic, road grit • primary treatment: separation of most organic solids from fluids • sludge treatment • secondary treatment: digestion and breakdown of remaining organic matter in the fluids • tertiary treatment: additional treatment to remove phosphates or bacteria

• primary sedimentation = the most important process • effluent is left to stand in large tanks where the faecal solids sink to the bottom so that they can be removed and treated separately • results in >95% org matter being removed from the fluid effluent so the risk of decomposition in the river or lake is greatly reduced

• screens: metal grills or sieves used to trap floating/suspended items like plastic and paper. These are then incinerated or disposed of in a landfill site • grit traps for stones and road grit: usually the channel widens out so that the effluent flows more slowly and the grit drops to the bottom as there is no longer enough kinetic energy to carry it along. The grit can later be removed from the tank then disposed of in a landfill site or by sterilisation and reuse • comminutors chop up suspended faecal solids, increasing the exposed surface area and speeding up later processes

• the sludge removed from the primary sedimentation tanks probs contain pathogens and its foul smell makes storage or disposal near urban areas difficult • to solve these problems, anaerobic digestion is used • anaerobic microbes digest the sludge in a warm digestion tank (anaerobic sludge digesters) for about 4 weeks • this kills most pathogens and the odours are reduced • the remains after this process has a smaller volume which can be disposed of in several ways

-LANDFILL: simple and relatively cheap but wastes nutrient content • DISPERSAL IN THE SEA relatively straightforward for coastal communities but most countries now ban this to reduce pollution • INCINERATION: a lot of fuel (usually nat gas) is required and is therefore expensive. Also creates further waste in the form of gas and a small amount of ash which is deposited in landfill sites • AGRICULTURAL USE: (see other card) • FUEL: an. dig. also produces biogas which is mainly methane with some CO2. This can be used as a fuel (e.g. to heat the digester, nearby buildings, or to generate electrictiy)

The sludge can be used as FERTILISER • it has a better C:N ratio, lower volume and lower odour than undigested sludge • important to time spreading carefully as application during the growing season would cover the crops, while application during the winter can cause damage to damp soils as farm vehicles compact the soil • heavy metals from urban wastes and road runoff may be present in the sludge and could be absorbed by crops and then be consumed with food. This can be reduced by adding lime to reduce the solubility of the heavy metals • remaining pathogens can be destroyed by heat treatment of the sludge before use

Destroys the small amount of organic matter that remains in the effluent from the primary sedimentation tank • AERATION TANKS/OXIDATION PONDS • SECONDARY SEDIMENTATION TANKS • TRICKLING FILTER BEDS

• the remaining organic matter in the fluid effluent is broken down by bacteria • shortage of oxygen can be a limiting factor as it slows down this aerobic process • to prevent this happening, large amounts of air are mixed in by paddle wheels, or air stones

• the effluent from the aeration tanks contains suspended bacteria which must not be wasted • these are collected in the secondary sedimentation tank and returned to the aeration tank as ‘activated sludge’ • in most sewage works, the clear effluent from secondary treatment is discharged into the river, lake, or sea • it should contain no pathogens or other organic materials, but it may contain some dissolved inorganic nutrients which could cause cultural eutrophication

• these provide an alternative process to aeration tanks • it is an older technique that has been largely replaced by the use of aeration tanks in activated sludge treatment • four rotating arms spray the liquid effluent over large cylindrical tanks containing lumps of a solid material such as gravel, coke, or blast furnace clinker • the surface area is maximised for bacteria, fungi, algae, worms, fly larvae and other invertebrates to digest remaining organic matter • nitrates may also be denitrified by bacteria so the liquid effluent will cause less eutrophication

Used when the discharge site for the treated effluent is particularly ecologically sensitive or important for humans • phosphates can be removed by adding a solution of iron(III) sulfate, producing insoluble iron phosphate as a fine sediment which can then be used as agri fertiliser • the effluent can be strained through very fine sieves called micro-strainers. The remaining suspended bacteria are killed by UV light or by adding a sterilising chemical such as chlorine

• volume of sewage remains relatively stable but volume of effluent received by sewage works can vary significantly with changes in weather e.g. storm/drought • sewage works are designed to cope with some extra flow but not the maximum flow that is possible, because it would be very expensive for only a few rare extreme storms • most sewage works have storm overflow tanks that can be used to hold surplus effluents after a storm. This is treated later when the volume of effluent arriving returns to normal

• majority sewage systems developed over the last 150 years • underground pipes were laid to collect all solid and liquid effluents often including drainage water from roads and roofs • originally these were discharged into the river or sea untreated, or onto fields in ‘sewage farms’ • sewage treatment works were added later • this approach produces large volumes of dilute sewage effluent

• have two separate waste collection systems • one collects only foul waste from toilets which requires full treatment but the smaller volume involved allows the construction of smaller and therefore cheaper sewage treatment works. It also means that the system is not affected by flow fluctuations caused by weather changes • the second system collects the larger volumes of cleaner water which requires little treatment before discharge

a substance/object capable of decaying naturally and in a way that isnt harmful, often decomposed by bacteria or other living orgs THEREBY AVOIDING POLLUTION

A mix of industrial and domestic waste in liquid form • water (up to 99.9%) • particulate organic waste e.g. food, goldfish • debris e.g. plastics • dissolved inorganic material e.g. N, P • dissolved organic material e.g. bacteria, wine, soap