Theory

Chemical oxygen demand (COD) is the measure of wastewater and water quality. This test is focused on the fact that a strong oxidizing agent, under acidic conditions can fully oxidize almost any organic compound to carbon dioxide. COD is equal to the equivalent amount of oxygen required to chemically oxidize substrate materials in water. The COD is often measured using a strong oxidant (e.g. potassium dichromate, potassium iodate, potassium permanganate) under acidic conditions. A known excess amount of the oxidant is added to the sample. Once oxidation is complete, the concentration of organics in the sample is calculated by measuring the amount of oxidant remaining in the solution. COD is expressed in mg/L, which indicates the mass of oxygen consumed per liter of solution.

Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose organic matter under aerobic conditions. Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, grass clippings, manure, sewage, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need to live. BOD also includes oxygen used to oxidize inorganic material such as sulfides and ferrous iron.

Coliform bacteria are found in the intestines of warm-blooded animals (including humans) also in plants, soil, air and water. Fecal coliforms are a specific class of bacteria, which only inhibit the intestines of warm-blooded animals. Their presence in drinking water indicates that disease-causing organisms (pathogens) could be in the water system. The coliform group of bacteria is the principal indicator of suitability of water for domestic, industrial, or other uses. Experience has established the significance of coliform group density as a criterion of the degree of pollution and thus of sanitary quality. Coliforms are Gram-negative, non-spore forming, oxidase-negative rods able to ferment lactose within 48 hours incubation at 35°C.

Total coliform is harmless and is generally found in the environment (vegetation). Total coliform is used as indicators to measure the degree of pollution and sanitary quality of well water, because testing for all known pathogens is a complicated and expensive process.

Nitrates (NO3-) are naturally occurring inorganic ions that are part of the nitrogen cycle. Microbial action in soil or water decomposes wastes containing organic nitrogen into ammonia, which is then oxidized to nitrite and nitrate. Because nitrite is easily oxidized to nitrate, nitrate is the compound predominantly found in groundwater and surface waters. Contamination with nitrogen-containing fertilizers (e.g. potassium nitrate and ammonium nitrate), or animal or human organic wastes, can raise the concentration of nitrate in water. Nitrate-containing compounds in the soil are generally soluble and readily migrate with groundwater. It is an essential nutrient for many photosynthetic autotrophs and thus a concern at wastewater discharge points.

Results

BOD

Initial value = 7.84mg/L

Final value = 0.17 mg/L

BOD concentration = [ (Initial – Final) x Volume of container] / Sample Amount

• Volume of container = 300ml

• Sample amount = 20ml

= [ (7.84 – 0.17) x 0.3] / 0.02

= 115.05 mg/L

Coliform

• Briliant Green = 10 positive = >23 (table value)

MPN/100ml = (Table MPN/100ml) x 10/Volume

=23 x 10/1

= 230MPN/100ml

• Coliform = 7 positive = 12 (table value)

MPN/100ml = (Table MPN/100ml) x 10/Volume

=12 x 10/1

= 120MPN/100ml

Nitrates

Recorded value = -0.2mg/L

NB: Refer to interferences in attachment in email in order to discuss the value recorded.

• Detergent used – Hilo Dishwashing Liquid

• Detergent contains – Biodegradable Anionic and Nonionic Surfactants. Contains no phosphates.

COD

Recorded value = 1455mg/L