Chemical oxygen demand COD

Under hot, acidic conditions, potassium dichromate oxidizes practically all organic substances as well as a number of inorganic components and ions. The level of oxidation depends on the type and concentration of the organic materials, the concentration of the potassium dichromate and sulphuric 

The analysis is carried out with an excess of potassium dichromate, whereby a part of the dichromate is reduced to the chromium (III) ion  

The excess of potassium dichromate ions is back-titrated against a ferrous solution using Ferroin as redox indicator  

This method is suitable for determining chemical oxygen demand in all types 

Certain organic substances which may be present in the water, e.g. benzene or pyridine, are not completely oxidized by the method quoted above. For this reason the COD value only reaches the 100 % limit of the TOD value (total oxygen demand) in specially favourable cases and may be considerably below this limit in waters which have an unfavourable make-up. 

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Several methods have been developed to estimate the oxygen demand in waste water treatment systems. Commonly used laboratory methods are biochemical oxygen demand (BOD), chemical oxygen demand (COD), total oxygen demand (TOD), total organic carbon (TOC), and theoretical oxygen demand (ThOD). 

Petrochemical units generate waste waters from process operations such as vapor condensation, from cooling tower blowdown, and from stormwater runoff. Process waste waters are generated at a rate of about 15 cubic meters per hour (m /hr), based on 500,000 tpy ethylene production, and may contain biochemical oxygen demand (BOD) levels of 100 mg/1, as well as chemical oxygen demand (COD) of 1,500 to 6,000 mg/1, suspended solids of 100 to 400 mg/1, and oil and grease of 30 to 600 mg/1. Phenol levels of up to 200 mg/1 and benzene levels of up to 100 mg/1 may also be present. 

Chemical oxygen demand (COD) A measure of the amount of oxygen, expressed in milligrams per liter, required to oxidize organie matter present in a substanee using a ehemieal oxidation method. 

The byproduct is a stoichiometric amount of 60 wt % H2S04, which is used in the chemical industry. The wastewater (0.3 m3/100 kg active matter), which contains paraffin, oxidation products of the paraffin, alkanesulfonate, and sulfur dioxide, has a chemical oxygen demand (COD) of 1800 mg/L and is readily biodegradable (>95% after 7 days). The sulfur dioxide emission after repeated washing of the off-gas amounts to 0.5 g/100 kg active matter [6]. 

Metal removal in SSFCWs has been recently focused on metal elimination from synthetic water and different wastewaters,66-86 on the evaluation of the effects of season, temperature, plant species, and chemical oxygen demand (COD) loading on metals removal,87 and on the accumulation of metals in wetland plant species and sediments.88-89 Recent reviews on heavy metal phytoremediation wetlands are also available.48... 

Because of the processes carried out in the plant, the expected compounds in wastewater are formaldehyde, urea, and polymers of these compounds. The global effluent of this kind of factory is characterized by a high chemical oxygen demand (COD) (due mainly to formaldehyde), relatively high values of nitrogen (arising from urea and copolymers) and a low content of phosphorus and inorganic carbon. The main characteristics of the effluent of a resin factory are showed in Table 19.1. 

Due to the large volumes of water used in pulp and paper processes, virtually all U.S. mills have primary and secondary wastewater treatment systems to remove particulates and BOD. These systems also provide significant removals (e.g., 30 to 70%) of other important parameters such as AOX and chemical oxygen demand (COD). 

Amuda, O.S. and Ibrahim, A.O., Industrial wastewater treatment for chemical oxygen demand (COD) sing natural material as adsorbent, African Journal of Biotechnology, 5 (16), 148-1487, 2006. 

The chemical composition of the soil and groundwater, specifically the amount of natural organic matter (NOM) and other reduced species, such as iron (II) or manganese (II) often analyzed as the chemical oxygen demand (COD) of the soil, or the soil oxidant demand. 

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