Introduction

The basic building blocks of the particles that make up our world are atoms. Atoms differ from each other by the number of protons in their nucleus, which gives them their specific properties (iron atom, hydrogen atom, oxygen atom, etc.). When atoms form a bond between them, a molecule is created. Molecules differ in the composition of the atoms from which they are formed and the way those atoms are bonded. Different molecules can be made of the same atoms, where the difference lies in the bonding structure.

Every atom has a charge (positive or negative), and atoms strive for the total net charge to be zero. Thus, if an atom is charged with -2, it will seek to bond with a +2 charge. For example, the basic charge of carbon is +4 and the basic charge of an oxygen atom is -2; in this case, a compound of one carbon atom with two oxygen atoms will be formed - Carbon Dioxide.

In water, a special state called an ionized state can exist, where there is no balance in charges, yet the water remains in a stable state.

We will now review the main parameters used in wastewater characterization.

*pH Level

A mathematical expression on a logarithmic scale of the H+ concentration in a solution. The charge of hydrogen is +1. If there are many hydrogen atoms in the solution, because of their positive charge, we will get a positive environment characteristic of an acidic environment that seeks to form bonds with negative atoms. On the other hand, as the concentration of positive hydrogen ions decreases, the pH (-log) rises, and we get a negative environment characteristic of an alkaline (basic) environment that seeks to form bonds with positive atoms.

pH is a measure of acidity/alkalinity. High levels of acidity or alkalinity are destructive to the environment.

The standard in Israel for effluents from on-site treatment plants is a pH between 6-10 so that they can be discharged into the sewage system.

Units of Substance Concentration in Solution:

There are several metrics to look at the concentration of substances in solution, the most familiar being mg/liter, or other mass-to-volume measurements. However, there is also a metric that measures the amount of particles (molecules/atoms) of a specific substance out of the total particles in the solution, such as the PPM - Parts Per Million index.

For example, a phosphorus concentration of 5 PPM indicates that in 1 kg of material, there are 5 mg of phosphorus. In the case of water, it is customary to treat PPM as equivalent to mg/liter. There are also particle counters for higher levels such as PPB - Parts Per Billion.

*Parameters for Organic Materials

Organic material is substance built from chains of carbon, oxygen, and hydrogen. The skeleton of the molecules is built of carbon, joined by atoms of oxygen and hydrogen, and sometimes other substances such as iron and nitrogen.

Measuring the amount of organic matter in wastewater is characterized by the oxygen consumption required to decompose it. This oxygen requirement is called COD - Chemical Oxygen Demand, and it is measured in mg of oxygen per liter (mg O2/liter).

In this test, we check how much organic matter can be oxidized until it undergoes a change into gaseous CO2.

This test is performed by aggressive oxidation of the solution and monitoring the amount of oxygen required for the process.

Total Organic Carbon (TOC). This parameter also checks the amount of organic material. This measurement is more difficult to perform and more expensive than COD. This measurement is used when salinity is very high and COD cannot be tested. The measurements are different: in COD we check how much organic matter can be oxidized, and in TOC we check the amount of carbon present in the solution. This metric is more accurate but harder to measure. A rule of thumb states that TOC is usually less than half of the COD.

Biochemical Oxygen Demand (BOD) – Biological oxidation of organic matter. This parameter checks how much oxygen is consumed by biology over several days (BOD1 – one day, BOD2 – two days, and so on). This is done by placing the material in a container and checking the amount of oxygen consumed over several days.

This allows us to quantify the amount of organic material degradable by biological factors in the solution.

*Nitrogen Parameters

The element nitrogen is abundant in the atmosphere and is not considered a pollutant, but organic nitrogen is considered a pollutant. There are several metrics for testing nitrogen:

Ammoniacal Nitrogen – All nitrogen bound in the form of ammonia (NH3/NH4+).

Total Kjeldahl Nitrogen (TKN) – This tests all forms of organic nitrogen and adds the nitrogen in ammonia form.

Total Nitrogen (TN) – This includes TKN as well as nitrogen in nitrite and nitrate forms, representing the most comprehensive measure of all nitrogen forms present in wastewater.

Specific parameters exist to detect materials with the potential to harm the environment or the wastewater treatment process at regional plants. Here are some of them:

Anionic Detergents – Negatively charged cleaning agents, often found in laundries. Detergents cause damage to the purification process, so it is necessary to check for their presence and prevent their discharge to the treatment plant.

Fats, Oils, and Grease (FOG) – Some fats are non-liquid, and this test is not simple. No technology exists today to perform this test easily. If we mix oil and water, we get clear separation, but oils can exist in an emulsion state, meaning they are integrated into the water to form a homogeneous liquid (e.g., milk, which is a type of emulsion).

Cyanides – A toxic substance formed by the bonding of carbon and nitrogen, mostly used in the metal processing industry. It is toxic to all living organisms, making it vital to prevent its discharge into the environment/sewer.

Sulfur – Sulfur has two common oxidation states: Sulfide and Sulfate.

Sulfide is a highly toxic gas used in small quantities in winemaking as a preservative. Sulfate is the oxidized state and is less toxic, hence the difference in permitted concentrations.

There are a wide variety of other standards for additional materials, all of which fall under the Water and Sewage Corporations Law (Industrial Wastewater).

We have summarized the essentials in the following table: If you have further questions on the subject, we invite you to contact us to get the answers.