Subjects of Study

Chlorophyll

Chlorophyll is the common name of a plant pigment capable of absorbing solar energy for the process of plant photosynthesis. Within plant cells, chlorophyll is organized distinctively, distributed in cytoplasm called chloroplasts. The molecular structure of chlorophyll comprises two parts: the porphyrin ring and the phytol (an

Fig. 15.2 Structure of Chlorophyll-a and Chlorophyll-b (Source: ysi.com)

acyclic hydrocarbon). The porphyrin ring is a strong chelating ligand created when four N atoms strongly associated with a metal atom (Mg) are coordinated in a planar arrangement (Fig. 15.2).

In nature, the two most common forms of chlorophyll are Chlorophyll-a (C55H72O5N4Mg) and Chlorophyll-b (C55H70O6N4Mg) with a ratio of Chlorophyll-a to Chlorophyll-b of 3:1.

There are several methods to determine chlorophyll:

– UV–vis photometry

– Fluorescence measuring

– High Pressure Liquid Chromatography (HPLC)

– Use of remote sensing images

BOD: Biochemical Oxygen Demand

BOD is the amount of oxygen demand for microorganisms to oxidate and stabilize dissolved organic or inorganic substances in water under certain conditions. Bacteria use dissolved oxygen (DO) for decomposition of organic matter and as a result DO will be reduced.

The oxidation of organic matter in water can occur in two phases:

– The first phase is mainly oxidation of hydrocarbon (HC). This phase occurs for 20 days at 20 °C

HC + O2 + Microorganism ® CO2 + H2 O

– The second phase is oxidation of nitrogen-containing compounds. This phase starts from the tenth day (or can start as early as the fifth day).

2NH3 + O2 + Microorganism ® 2NO - + 2H2 + 2H2 O

2NO -2 + O2 + Microorganism ® 2NO3

BOD is the single most important parameter to assess water pollution. The higher the BOD concentration, the more biodegradable organic matter exists. A typical concentration might be “BOD5” which is oxygen demand to oxidate biodegradable organic matter at 20 °C for 5 days.

COD: Chemical Oxygen Demand

COD is the amount of oxygen demand to oxidate organic matter fully in water. It is a parameter for both organic matter easily susceptible to biodegradation and organic matter that resists biodegradation. Thus, COD is determined by the photometric method with strong oxidizing reagents in an acid environment and involvement of Ag2SO4 as a catalyst.

This method allows COD to be determined from 10–500 mg/L in 2 h.

Phosphorus

Phosphorus exists in water in many forms: ortho phosphate (PO 3−), polyphosphate

4− 5−

(P2O7, P3O10) and organic phosphorus. In addition, bio-inorganic and organic phosphorus is found in sediment and sludge. Phosphorus is one of the nutritional components necessary for the life of organisms, especially aquatic life.

Ortho phosphate is determined by the photometric method with a vanadate molybdate reagent.

PO4+VO -3+11MoO4 + 25H+ ®H3 PVMo O +11H2 O

Nitrogen

Nitrogen exists in water in several forms:

– Ammonium (NH +): The metabolic product of nitrogen-containing compounds in wastewater.

NH3 + H+® NH +– Nitrate (NO3 ): In a low pH environment, NH3 is metabolized to NH4 and oxi-dized to NO3 by oxygen.

NH4+ + 2O ® H O + 2H+– Nitrite (NO −) The intermediate product of the nitrogen cycle, nitrite is toxic to fish and other aquatic life.

Determination of nitrogen is based on the principle of oxidizing samples to produce the ammonium form of nitrogen.

NH4++ OH-® NH3 + H2 O

HBO2 +NH3 = NH4+BO2

Ammonium is determined using titrate BO2with HCl 0.01N:

BO2-+H+ + = HBO

 
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