What is WASTEWATER?REPORTER: Grace T. Superales

“Sewage”Originates from household wastes, human and animal wastes, industrial wastewaters, storm runoff, and groundwater infiltration.

Characteristics of Wastewater

PHYSICAL CHEMICALBIOLOGICAL

Physical Properties of Wastewater

FACTORS:Temperature

affects chemical reaction and biological activities

Solids Concentrationcomprise matter suspended or dissolved in water and wastewater.

affects the operation and sizing of treatment units

TOTAL SOLIDS (TS)

The sum of total suspended solids (TSS) and total dissolved solids (TDS)

It is the material left in the evaporation dish after it has dried for at least 1h or overnight (preferably) in an oven at 103 to 105˚C.

Where:A = weight of dried residue plus dish, mg

B = weight of dish, mg1000 = conversion of 1000 mL, L

(6.1)

TOTAL SUSPENDED SOLIDS (TSS)

Nonfilterable Residue It is a very important quality parameter for water and wastewater.

It is determined by filtering a well-mixed sample through a 0.2 mm pore size, 24 mm diameter membrane; the membrane filter is placed in a Gooch crucible, and the residue retained on the filter is dried in an oven for at least 1h at a constant weight at 103 to 105°C.

Where:C = weight of filter and crucible plus dried residue, mg

D = weight of filter and crucible, mg1000 = conversion of 1000 mL, L

(6.2)

TOTAL DISSOLVED SOLIDS (TDS)

Filterable ResidueTotal dissolved solids in raw wastewater are in the range of 250 to 850 mg/L.

TDS is determined as follows. A well-mixed sample is filtered through a standard glass fiber filter of 2.0 mm normal pore size, and the filtrate is evaporated for at least 1h in an oven at 180±2˚C. The increase in dish weight represents the total dissolved solids.

Where:E = weight of dried residue plus dish, mg

F = weight of dish, mg1000 = conversion of 1000 mL, L

(6.3)

FIXED AND VOLATILE SOLIDS

The residue from TS, TSS, or TDS tests is ignited to constant weight at 550˚C. The weight lost on ignition is called volatile solids, whereas the remaining solids represent the fixed total, suspended, or dissolved solids.

Where:G = weight of residue plus crucible before ignition, mg

H = weight of residue plus crucible or filter after ignition, mg

I = weight of dish or filter, mg

(6.4)(6.5)

SETTLEABLE SOLIDS

Is the term applied to material settling out of suspension within a defined time.

Settled solids may be expressed on either a volume (mL/L) or a weight (mg/L) basis.

EXAMPLE

A well-mixed 25 mL of raw wastewater is used for TS analyses. A well-mixed 50 mL of raw wastewater is used for suspended solids analyses. Weights (wt.) of evaporating dish with and without the sample either dried, evaporated, or ignited were determined to constant weight according to Standard Methods (APHA et al., 1998). The laboratory results are

Wt. of evaporating dish = 42,472.3 mgWt. of dish plus residue after evaporation at 105°C = 42,498.6

mgWt. of dish plus residue after ignition at 550°C = 42,486.3 mgWt. of filter plus Gooch crucible = 21,530.8 mgWt. of residue and filter plus crucible after drying at 105°C =

21,544.7 mgWt. of residue and filter plus crucible after ignition at 550°C =

21,534.9 mgCompute the concentrations of total solids, volatile solids, fixed solids, totalsuspended solids, volatile suspended solids, and fixed suspended solids.

Chemical Constituents of Wastewater

Organic Matter carbohydrates, fats, oils, grease, surfactants, proteins, pesticides, and other agricultural chemicals, volatile organic compounds, and other toxic chemicals (household and industrial)

Inorganic Matterheavy metals, nutrients (nitrogen and phosphorus), pH, alkalinity, chlorides, sulfur, and other inorganic pollutants

Gases carbon dioxide, nitrogen, oxygen, hydrogen sulfide, and methane

The strength (organic content) of a wastewater is usually measured as:

5-days biochemical oxygen demand (BOD5)

chemical oxygen demandtotal organic carbon

BOD5 Test

It measures the amount of oxygen required to oxidize the organic matter in the sample during 5 days of biological stabilization at 20°C.

The ratio of carbon, nitrogen, and phosphorus in wastewater is very important for biological treatment processes, where there is normally a surplus of nutrients.

BOD/N/P = 100/5/1100 mg/L BOD to 5 mg/L nitrogen to 1 mg/L phosphorus

COD Test

It is a measurement of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant, such as potassium dichromate.

The COD test takes 3 to 4 h rather than 5 days for BOD data.

The normal COD range for raw wastewater is 200 to 600 mg/L

TOC Test

TOC is a sum measure of the concentration of all organic carbon atoms covalently bonded in the organic molecules of a given sample of water.

It will detect the presence of all carbon-bearing molecules, thus identifying the presence of any organic contaminants.