Total Solids in wastewater come from adding TSS and TDS, giving the full picture.

Total solids in wastewater are a big deal. They’re the sum of everything solid that’s left in the water—both what’s floating around and what’s dissolved away. For engineers and students, breaking that down helps you understand how water moves through treatment, how sludge forms, and what the plant must remove to meet standards. So, what exactly goes into Total Solids, and how do we calculate it?

What TS, TSS, and TDS actually mean

• Total Solids (TS): the combined mass of all solids in a water sample, whether they’re suspended or dissolved.

• Total Suspended Solids (TSS): the solids that stay in suspension. These are the particles that don’t settle out in a simple sedimentation tank.

• Total Dissolved Solids (TDS): the solids that are dissolved in the water—minerals, salts, organic molecules that pass right through a filter and remain in solution.

Here’s the key relationship you’ll see on boards, in lab manuals, and in plant reports: TS = TSS + TDS. In other words, if you know how much solids are suspended and how much are dissolved, you’ve got the full picture of total solids.

Why this matters in the real world

Understanding TS helps operators predict how wastewater will behave in treatment units. Suspended solids influence how well settling tanks work, how much sludge you’ll generate, and how you design filtration or clarification stages. Dissolved solids can affect membrane fouling, corrosion, taste and odor, and the efficiency of certain biological processes. Regulators often set limits on both TSS and TDS (and thus TS) for discharge or reuse. So knowing how to quantify TS is less about passing a test and more about making sure water leaving a plant is clean and safe.

How TS is calculated in practice

Think of TS as a quick math check that combines two specific lab measurements: TSS and TDS. The formulas are straightforward, but the measurement steps require careful technique.

Step 1: Measure TSS (suspended solids)

• Take a known volume of wastewater (commonly 1 liter, but methods vary by lab or regulatory guidelines).

• Filter the sample through a pre-weighed glass fiber filter. The solids that stay on the filter are your suspended solids.

• Dry the filter with the retained solids in an oven at 103–105°C until a constant weight is reached. This usually means drying, weighing, and repeating until the weight stops changing.

• Weigh the dried filter plus solids, then subtract the mass of the empty filter. The result is the mass of TSS in that known volume of water.

• Convert to a concentration, typically milligrams per liter (mg/L), by dividing the solid mass by the sample volume.

Step 2: Measure TDS (dissolved solids)

• Take a known volume of wastewater (again, 1 liter is common, or the volume specified by your method).

• Place the sample (or a known aliquot) in a small porcelain dish or crucible, then evaporate the water off in an oven until only the dissolved solids remain. This is the drying step that leaves the residue behind.

• Cool and weigh the dish with the dried residue. Subtract the mass of the empty dish to get the mass of TDS in that volume.

• Convert to mg/L, just like with TSS.

Step 3: Compute TS

• Add the two results: TS (mg/L) = TSS (mg/L) + TDS (mg/L).

Practical example to bring it to life

Suppose you measure TSS as 120 mg/L and TDS as 300 mg/L in a 1-liter sample. Add them together and you get TS = 420 mg/L. Simple arithmetic, but it paints a complete picture: more solids in the water, more work for treatment units, and more material to manage in sludge.

A few notes on method details

• Units matter. Keep it consistent. If you report TSS and TDS as mg/L, TS will also be mg/L.

• Temperature and drying time matter for TSS. You want a constant weight, not a fluctuating number due to incomplete drying.

• For TDS, ensure the evaporation step leaves only dissolved solids. If you don’t fully evaporate the water, you’ll underestimate TDS and TS.

• Calibration and blank corrections are essential in both measurements. A clean, pre-weighed filter and a properly tared dish aren’t glamorous, but they’re the difference between accurate numbers and guesswork.

• Samples should be handled carefully. If a sample sits too long, solids can settle, or reactions can change the dissolved content. In practice, labs often analyze promptly or preserve samples to minimize changes.

Common sense tips to keep measurements honest

• Use fresh, clean glassware and filters; even tiny residues can skew results.

• Verify the oven’s temperature and ensure it reaches and holds the target range consistently.

• Run a blank (no sample) filter and a known standard so you can check for drift in the balance or drying procedure.

• Report both TSS and TDS when you can; it helps downstream operators and designers interpret the TS value accurately.

• If your plant uses alternative methods, make sure your equations line up with the specific procedure and units used there.

Why the separation matters in the first place

• Suspended solids influence settling and clarification. Platforms like primary tanks and clarifiers are designed to remove these particles by gravity or flotation.

• Dissolved solids affect processes that can’t be solved by settling alone. They influence membrane performance, chemical dosing, and sometimes disinfection efficiency.

• In design and compliance, regulators often want to see how much is floating versus dissolved. TS is a concise, all-encompassing figure, but knowing the split (TSS and TDS) lets engineers tailor treatment steps precisely.

Common pitfalls and how to avoid them

• Mixing up TSS and TDS. It happens when you’re juggling multiple samples and quickly jot numbers. Double-check: TSS is the solid on the filter; TDS is the dissolved material left after evaporation.

• Incomplete drying. If you think you’re done after the first weigh, you might be off. Do the constant-weight check.

• Inaccurate volume control. If your sample isn’t exactly the volume you think, your mg/L values will be off. Use calibrated pipettes or volumetric flasks.

• Unit confusion at the calculator. A quick check: mg/L, not mg or g without the right conversion factor.

• Ignoring sample preservation. Some samples change between collection and analysis. Use recommended preservation practices if there’s a delay.

Real-world relevance: what this means for treatment plants

• TS guides process control. If TS climbs, you may need more robust sludge handling or different dosing schemes for coagulants and flocculants.

• It informs regulatory compliance. Discharge permits often set limits on TSS, TDS, or TS. Clear, accurate numbers help ensure you stay within permitted boundaries.

• It shapes operator decisions. A plant with high TSS might see strain on clarifiers, while high TDS could signal the need for desalination steps or pretreatment adjustments.

A quick recap you can hang your hat on

• Total Solids (TS) equals Total Suspended Solids (TSS) plus Total Dissolved Solids (TDS).

• TSS is measured by filtering a known volume, drying the retained solids, and weighing.

• TDS is measured by evaporating water from the sample and weighing the remaining solids.

• TS = TSS + TDS, with the result typically expressed in mg/L.

• Proper technique, calibration, and timely analysis matter for accuracy and downstream usefulness.

A little big-picture reflection

Water treatment is a balancing act. On one side are the floating, visible solids that clog pipes and settle in tanks; on the other side are the microscopic dissolved constituents that quietly shape chemical reactions and membrane performance. Total Solids give you a single, honest snapshot of both worlds. When you hold that snapshot in your hands, you’re better equipped to design, operate, and optimize treatment in ways that protect public health and the environment.

If you’re curious to see how labs translate these concepts into everyday practice, you’ll notice a recurring theme: careful measurement, disciplined procedure, and a pinch of scientific intuition. It’s not about chasing perfection; it’s about getting reliable numbers you can trust to make real-world decisions. And that’s the kind of knowledge that makes wastewater fundamentals feel, well, meaningful.

In short: TS is a straight sum of TSS and TDS. TSS covers the solids that stay put in filtration, and TDS covers what’s dissolved. Add them, and you’ve got the full load of solids in your sample. With that clarity, you’re ready to interpret and act on the data with confidence.