Envi Chapter 3

University of San Carlos - Department of Chemical Engineering

University of San Carlos - Department of Chemical Engineering

Self-Purification Mechanisms Physical Process Chemical Process Biological Process

Speed and Completeness of the Process Depend on: Volume, rate, turbulence of flow, physical characteristic of bottom and bank material, variations in sunlight and temperature and the chemical nature of the natural water

University of San Carlos - Department of Chemical Engineering

Physical Processes Dilution Mixture, CM

QS

QM Stream, CS

QW Waste, CW

Dilution Capacity

C S QS +CW QW =C M QM

University of San Carlos - Department of Chemical Engineering

Sedimentation and Resuspension Nature’s method of removing suspended particles

Drawbacks Anaerobic conditions will develop Alter the streambed by filling up the pore space Create unsuitable conditions for the reproduction of many aquatic life Development of banks of silt and mud Reduce reservoir storage capacity Increase flooding

University of San Carlos - Department of Chemical Engineering

Filtration Gas Transfer Solubility Extent to which the gas is soluble in the water

Henry’s Law

P x= H

H – the coefficient of absorption P – pressure of the gas above the liquid

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Transfer Rate The rate at which dissolution or release occurs

dC = ( Cs − C ) k a dt dC/dt – the instantaneous rate of change of the concentration of the gas in the liquid Cs and C – saturation concentration and the actual concentration

Two-film model of the interface between gas and liquid: (a) absorption mode and (b) desorption mode.

University of San Carlos - Department of Chemical Engineering

Heat Transfer Heat Increase Decrease the number of species of aquatic plants and animals Affect ionic strength, conductivity, dissociation constants, solubility and corrosion potential

University of San Carlos - Department of Chemical Engineering

Chemical Processes Chemical Conversions Accessibility of the essential nutrients

Fe 3+ +PO4

3−

→FePO4

Stabilization of pH

H 2O + CO2 ⇔ H 2CO3 *

+

*

H 2CO3 ⇔ H + HCO3 +

2+

−

CaCO3 + H ⇔ Ca + HCO3

−

University of San Carlos - Department of Chemical Engineering

Biochemical Processes Activation energy can be supplied by microorganisms that utilize biodegradable organics and nutrients for food and energy

Metabolism Sum of the processes by which living organisms assimilate and use food for subsistence, growth, and reproduction

Metabolic Processes Catabolism

- provides the energy for the synthesis of new cell - provides maintenance of other cell functions

Anabolism

- provides the material necessary for cell growth

Endogenous Catabolism

- used of stored food for maintenance energy

Catabolism

ain En tena erg nce y

New Cells (biomass)

Endogenous catabolism

M

Organics + microorganisms

gy for r e n E ction u d o r rep

University of San Carlos - Department of Chemical Engineering

Anabolism

Energy

+

Waste products

Waste heat

Generalized metabolic pathway.

Organic residue

University of San Carlos - Department of Chemical Engineering

Enzymes - organic catalysts that influence reactions without becoming a reactant themselves - lower activation energy necessary to initiate reactions - complex protein compounds and are very specific in terms of reactions

Constitutive Enzyme Enzymes are a normal part of a particular microorganism

Adaptive Enzyme Exposed to unusual substances

Energy Transfer Model ATP

Catabolism

Anabolism ADP + P

University of San Carlos - Department of Chemical Engineering

Microorganisms in Natural Water Systems Protista Organisms in which there is no cell specialization

Bacteria - the primary decomposers of organic material - single-cell protists that utilize soluble food - chemical formula: C5H7O2N

Classification of Bacteria Autotrophs Derive both the energy and material sources from inorganic sources

Heterotrophs Obtain both energy and material from organic compounds

Phototrophs Utilize sunlight for an energy source and inorganic substances for a material

University of San Carlos - Department of Chemical Engineering

Aerobic Heterotrophs Require oxygen in their metabolic processes

Anaerobic Heterotrophs Utilize organics in the absence of oxygen

Facultative Heterotrophs Function as aerobes when oxygen is present but switch to anaerobic processes when oxygen becomes unavailable

Protozoa - single-cell organisms that reproduce by binary fission - ingest solid organics for food - obtain both energy and material for growth and reproduction from the same organic food source

Ciliata Most important protozoal group in natural water systems

University of San Carlos - Department of Chemical Engineering

Algae - autotrophic, photosynthetic organisms - metabolize the waste products of heterothrophic bacteria in the in the presence of sunlight - negative effect: produce oily substances that cause taste and odor

Other Organisms Rotifers and Crustacea - lower-order animals that prey on bacteria, protozoa, and algae - help to maintain a balance in the populations of primary producers - Serve as an important link in the food chain

Sludge Worms, Helminths and Insect Larvae - feed on sludge deposits and help break down and solubilize the particulate organics

University of San Carlos - Department of Chemical Engineering

Response of Streams to Biodegradable Organic Waste

Chemical Process Biological Process

Conversion Process

Physical Process

Removal Process

Work Simultaneously

University of San Carlos - Department of Chemical Engineering

Dissolved-Oxygen One of the most important constituents of natural water systems

Two Mechanisms to Contribute Oxygen to Surface Water Dissolution of Oxygen from the Atmosphere (Reaeration) Production of Oxygen by Algal Photosynthesis

Reaeration Oxygen Deficit

D = CS − C

Where D – dissolved oxygen deficit CS and C – equilibrium and actual oxygen concentration

dD dC =− dt dt

University of San Carlos - Department of Chemical Engineering

Algal Photosynthesis

CO2 + 2 H 2O light →  CH 2O + O2 + H 2O new algal cells

In the Absence of Light

CH 2O + O2 → CO2 + H 2O

University of San Carlos - Department of Chemical Engineering

Bacterial Cell Composition Element

Dry Weight, %

Carbon

50

Oxygen

20

Nitrogen

14

Hydrogen

8

Phosphorus

3

Sulfur

1

Potassium

1

Sodium

1

Calcium

0.5

Magnesium

0.5

Chlorine

0.5

Iron

0.2

All Others

0.3

University of San Carlos - Department of Chemical Engineering