Biodegradable Wastes The biodegradable wastes are those that

• Biodegradable Wastes - The biodegradable wastes are those that can be decomposed by the natural processes and converted into the elemental form. For example, kitchen garbage, animal dung, etc. • Non-biodegradable Wastes - The non-biodegradable wastes are those that cannot be decomposed and remain as such in the environment. They are persistent and can cause various problems. For example, plastics, nuclear wastes, glass, etc.

Biochemical Oxygen Demand (BOD)

BOD • BOD: The amount of oxygen used by microbes in the oxidation of organic matter • BOD is the most important parameter in water pollution control. As an indication of the quality of water • Determines the pollution strength of domestic and industrial wastes in terms of the oxygen that will be required if discharged into natural watercourses in which aerobic conditions exist. • Quantitative relationship between amount of oxygen required to convert an amount of organic compound to carbon dioxide, water and ammonia:

BOD measurement • The BOD sample is measured by determining the amount of O 2 consumed from a sample of water placed in a BOD bottle (air tight container) and kept in incubator (temperature 20 o. C, no light) for 5 days. • Light must be excluded to prevent algal growth that may produce O 2 in the bottle • BOD may be measured directly in a few samples but in general a dilution is required

• Calculation of BOD 1) BOD 5 (mg/L) = D 1 -D 2 (when no seed or dilution is used) D 1=initial DO in sample D 2=final DO in sample 2) BOD (mg/L) = (D 1 -D 2)/P (when unseeded dilution water is used) P= Vol. sample/vol. mixture P= m. L pipeted/300 m. L 3) BOD (mg/L) = [(D 1 -D 2)-f(B 1 -B 2)]/P (when seeded dilution water is used) B 1=initial seed DO in control B 2=final seed DO in control f = fraction of seed in the incubated sample It is learned that it is not statiscally reliable to base BOD values upon depletion that produce a depletion of oxygen less than 2 mg/L. Only use DO data range 2 -7 mg/l. At the end, at least 0. 5 mg/l

BOD measurement • To ensure that all other conditions are equal, a very small amount of micro-organism seed is added to each sample being tested. This seed is typically generated by diluting activated sludge with de-ionized water/dilution water. • Diluting the sample with oxygen saturated de-ionized water, inoculating it with a fixed amount of seed, measuring the dissolved oxygen (DO) and then sealing the sample to prevent further oxygen dissolving in. • The sample is kept at 20 °C in the dark to prevent photosynthesis for 5 days, and the DO is measured again. The difference between the final DO and initial DO is the BOD. • The loss of dissolved oxygen in the sample, once corrections have been made for the degree of dilution, is called the BOD 5.

• Dilution water: - phosphate buffer, Mg. SO 4, Ca. Cl 2, and Fe. Cl 3 solutions - before use, bring dilution water temperature to 20 + 3°C. Saturate with DO by shaking in a partially filled bottle or by aerating with organic-free filtered air.

Application of BOD data • Principle test applied to domestic and industrial waste to determine strength in terms of oxygen required for stabilization • Serves regulatory authorities in monitoring the quality of streams and effluents discharged into such waters • Important consideration in design and costs of biological treatment facilities

Chemical Oxygen Demand (COD)

COD • COD is used to measure organic strength of domestic and industrial wastes • Waste is measured in terms of the total quantity of oxygen required for oxidation to carbon dioxide and water • Based upon fact that all organic compounds can usually be oxidized by strong oxidizing agent under acid conditions. • COD limitation: inability to differentiate between biologically oxidizable or inert organic matter • COD advantage: the short time required for evaluation (3 h)

COD by dichromate • Potassium dichromate is a cheap, very potent oxidizing agent in solutions that are strongly acidic • The reaction involved may be represented as follows: where d = 2 n/3 + a/6 – b/3 – c/2 • COD are reported in terms of mg of oxygen

Measurement of excess oxidizing agent • An excess of oxidizing agent must be present to ensure all organic matter is oxidized completely within oxidizing agent’s power • Ferrous ion (ferrous ammonium sulfate) is used to reduce excess dichromate • The reaction between ferrous ammonium sulfate and dichromate: indicator Ferroin is added during this titration step

COD measurement: volumetric and colorimetric methods • VOLUMETRIC: Reducing agent is used to determine how much oxidizing agent was used in oxidation of organic matter • COLORIMETRIC: change during organic oxidation from orange color of Cr (VI) [absorbs at wavelength 600 nm] to blue color of Cr (III) [absorbs at wavelength 420 nm]

Application of COD data • Extensively used in analysis of industrial wastes as results may be obtained in short time rather than BOD • May be used to indicate toxic conditions and presence of biologically resistant organic substances in conjunction with BOD test

• COD/BOR removal

Solids

Solids • All matter except water contained in liquid materials is classified as solid matter • General definition: Matter that remains as residue upon evaporation and drying at 103 - 105 C • There’s various kinds of solids present; dissolved, suspended, volatile and fixed

TS, TDS, TSS • Total solids (TS) in a liquid sample consist of total dissolved solids (TDS) and total suspended solids (TSS). • The total dissolved solids represents all materials in the water that will pass through a filter with a 2. 0 µm or smaller average pore size. • The material retained on the filter represents TSS. • The measurement of total solids is conducted at 103 - 105 C, while water supplies samples were dried at 180 C for total dissolved solids analysis

Volatile (VS) and fixed solids • Sample undergoes combustion procedure in furnace, in which organic matter is converted to gaseous CO 2 and H 2 O. • Temperature is accurately controlled to prevent decomposition and volatilization of inorganic substances as much as consistent with complete oxidation of organic matter • Standard procedure for volatile-solids analysis is to conduct ignitions at 550 C -about the lowest temp. at which organic matter can be oxidized at reasonable speed -decomposition of inorganic salts is minimized • If ignitions are properly performed, the weight loss incurred reasonably accurate measure of organic matter (VS) for most municipal sludges and the residue remaining as ash or fixed solid (inorganic materials)

crucible Generalized schematic of steps to determine TS, VS, and FS.

• Solid removal

Solids analyses of interest in water quality control • The amount of dissolved solids in water determine the suitability for domestic use • In municipal water supplies with total-solids content greater than 500 mg/L imparts taste to the water and sometimes cause effect on some people. • The SS analysis is used to evaluate the strength of domestic ww and to determine the efficiency of treatment unit • Settleable solids analysis is used extensively to determine the need for and design of primary settling tanks for industrial wastewaters, and for determining the efficiency of sedimentation units.