Wastewater Total Dissolved Solids Characterization

[Kodiak31]

I’m working on a loading analysis to quantify and likely characterize Total Dissolved Solids in a food manufacturer’s waste stream. The food manufacturer will need to pretreat to a local limit for BOD (easy part) and potentially TDS (hard part) before the local municipality will accept sewage.

Spot sampling has indicated some waste streams (brines and juices) are very high in TDS. The remaining waste streams need to be tested.

A few questions:

Other than simply testing for TDS, is there a specific testing regimen which should be performed to identify the constituents of the TDS in each waste stream (e.g., sodium, chloride, calcium, etc.)? Is there a standard battery of tests? What else specifically should I be looking for to help assess treatment options if required?

If a filter/gravimetric TDS test is performed on a waste stream likely to be high in dissolved sugar (e.g., fruit juice), would this test be picking up soluble BOD from the sugar that would likely be treated aerobically in a pretreatment system? In my mind, this should be separated from the ionized dissolved solids which will be more difficult to treat. Is there a way to test these independently?

 

[bimr]

You want a water chemistry analysis. If the TDS is high, the elements causing the TDS are likely to be sodium chloride.

In addition, you should request a COD test and a BOD test. These tests are used to determine if the waste is biodegradable.

You should also investigate the pretreatment requirements of the local wastewater treatment authority. There may be some discharge parameters that are not typically included in the standard water chemistry test.

 

[Kodiak31]

Is there any standard or agreed upon definition of what constitutes a "standard water chemistry test"?

 

[bimr]

You should obtain a complete analysis in the beginning of your project so you don't miss a potential problem. Later, you can just repeat the analysis for the areas where the problems are. The amount of sugar in the wastewater will be represented in the BOD test. Typical list of parameters looks like this:


1 pH
2 Conductivity
3 Turbidity
4 Total Hardness
5 Calcium
6 Magnesium
7 Chloride
9 Total Alkalinity
9 Sulfate
10 Sodium
11 Potassium
12 Silica
13 Ammonia
14 Nitrate
15 Nitrite
16 Organic Nitrogen
17 Total Nitrogen
18 Total Dissolved Solids
19 Total Suspended Solids
20 Volatile Suspended Solids
21 Temperature
22 CO2
23 BOD
24 COD
25 TOC
26 Phosphate
27 Oil and Grease
28 Iron ppm
29 Manganese ppm
30 Total Chromium ppm
31 Nickel ppb
32 Nickel ppm
33 Copper ppb
34 Copper ppm
35 Zinc ppm
36 Cyanide
37 Aluminum ppm
38 Lead ppb
39 Cadmium ppm
40 Silver ppb
41 Mercury ppb
42 Tin
43 Boron
44 Barium
45 Beryllium
46 Bromate
47 Bromine
48 Fluoride
49 Antimony
50 Molybdenum ppm
51 Arsenic ppb
52 Selenium ppb
53 Vanadium
54 Phenol

 

[Kodiak31]

Very helpful. I don't think I will need all of these tests given the nature of the waste stream, but a great place to start.

With respect to the BOD test, I want to quantify how much of the TDS is dissolved ionized solids that are difficult to treat, versus how much is dissolved sugar, etc. that would be easy to treat biologically. The BOD test will give me an oxygen requirement necessary for the biological treatment, but won't tell me directly what fraction of the TDS is biologically treatable. Is my best approach to simply test for all ionized solids (Na+, Cl-, K+, etc.) and compare this to the total gravimetric TDS? Then assume the difference represents the dissolved components (e.g., sugar) that can be treated biologically?

 

[bimr]

What you want to do is to compare the results of the COD test to the BOD test. The ratio of these two parameters is a measure of the biodegradability. If the COD:BOD ratio does not exceed 2:1, the biodegradability is said to be good. Higher values indicate the presence of poorly biodegradable substances. A typical value of COD/BOD for municipal sewage effluent is often < 2.

It is a good idea to do an initial scan for all of the parameters at the beginning to rule out potential issues.