Environmental Biophysics


Biophysics is an interdisciplinary science using methods of, and theories from physics to study biological systems

Biophysics deals with all scales of biological organization, from the molecular scale to whole organisms and ecosystems

Often overlaps with biochemistry, bioengineering, computational biology etc

 It has been suggested as a bridge between biology and physics

The term "biophysics" was originally introduced by Karl Pearson in 1892

  Mass Balance

When a chemical reaction takes place, mass is neither created nor destroyed (exception nuclear reaction)

The Law of Conservation of Mass states that matter can be changed from one form into another, mixtures can be separated or made, and pure substances can be decomposed, but the total amount of mass remains constant

Environmental application – track pollutants

  Mass Balance (Steady & Conservative State)

Mass Balance (steady state)

At steady state / equilibrium, nothing is changing (input constant, pollutant concentration constant). But the decay process is going on which changes the form of material.


Mass Balance (Conservative)

Substance is conserved. No decomposition (bacterial, radioactive, chemical reaction etc). Example, TDS in water, Heavy metals in soil, CO2 in air


  Steady State Conservative System

If there is no change, no reaction and accumulation in system then the total input becomes the output.


therefore 20X10 + 40X5  = 400

  Steady State Non-Conservative System

In this case as the system is non conservative therefore the output totally depends on how much material has been decayed in the system which depends on decay rate

What is the rate of decay??? it depends on chemical kinetics

First order reaction :

Rate of loss of substance is proportional to amount of substance present

dC/dt = -K C (C=concentration, V = Volume)

Concentration C is uniformly distributed in Volume V

Decay Rate = K C V

Input Rate = Output Rate + K C V

The output depends on the order of reaction

Zeroth-order reaction is one whose rate is independent of concentration; its differential rate law is rate = k.


First-order reaction, the reaction rate is directly proportional to the concentration of one of the reactants. First-order reactions often have the general form A → products. The differential rate for a first-order reaction is as follows:


Second-order reaction  is one whose rate is proportional to the square of the concentration of one reactant. These generally have the form 2A → products. A second kind of second-order reaction has a reaction rate that is proportional to the product of the concentrations of two reactants. Such reactions generally have the form A + B → products

The differential rate law for the simplest second-order reaction in which 2A → products is as follows:


  Laws of Thermodynamics

Energy Balance

Energy is capacity to do work, where work is described as product of force and displacement. There is always inefficiency in work thus loss of energy (2nd Law of Thermodynamics). Power is the rate of doing work (energy per unit time) J/s/Watt, kJ/s,

First law of Thermodynamics

The law of conservation of energy

It states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed

The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings

When heat is added to a system, some of that energy stays in the system and some leaves the system. The energy that leaves does work on the area around it. Energy that stays in the system creates an increase in the internal energy of the system. 


  • Chemical energy to heat / electricity in power plant
  • Mechanical energy to electricity in Dams

Second law of Thermodynamics

Energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. Whenever there is an interaction between energy and matter, thermodynamics is involved. Some examples include heating and air‐conditioning systems, refrigerators, water heaters, etc.

No reaction is 100% efficient. Some amount of energy in a reaction is always lost to heat. Also, a system can not convert all of its energy to working energy. Says that there will always be some waste heat/energy, it is impossible to devise a machine that can convert heat to work with 100% efficiency


  • Thermal Power Plant- the example shows the loss of energy in form on heat that is the reason for increase in outlet water. The loss thus affects the efficiency of the plant.

Efficiency - Steam Plant


  Carnot Heat Engine

The most efficient heat engine that could possibly operate between the two heat reservoir is called a Carnot Engine

A heat engine acts by transferring energy from a warm region to a cool region of space and, in the process, converting some of that energy to mechanical work. The cycle may also be reversed. The system may be worked upon by an external force, and in the process, it can transfer thermal energy from a cooler system to a warmer one, thereby acting as a refrigerator or heat pump rather than a heat engine.

Similar work is done in OTEC

  Ocean Thermal Energy Conversion (OTEC)

Ocean thermal energy conversion(OTEC) uses the temperature difference between cooler deep and warmer shallow or surface ocean waters to run a heat engine and produce electricity

OTEC works best when the temperature difference between the warmer, top layer of the ocean and the colder, deep ocean water is about 36°F (20°C)