BOD5 at 20 Degrees C: What the Five-Day Number Measures, Where It Misleads, and How to Run It Properly

2026-10-08

The five-day BOD test is a centenary-old convention that measures microbial appetite rather than chemical mass, and it still drives process selection through the BOD/COD ratio. This piece covers why 20 degrees C and five days became standard, the benchmar

Residual Chlorine in Practice: From Tap Standards and Pool Limits to Dechlorination Before Reverse Osmosis

2026-10-08

Residual chlorine means three different things depending on whether it is free, combined or total, and each fraction has its own limit in drinking water, pools, foot baths and medical effluent. This piece sets out the standards side by side, compares DPD

Coking Effluent and the 0.3 Biodegradability Wall: Picking Between Biofilm A/O, AOP and Zero Discharge

2026-10-08

Coking effluent carries roughly 500 identified compounds, surplus nitrogen and a BOD5/COD ratio near 0.3, which caps what biology can do on its own. This piece walks the numbers that decide the flowsheet, why plain activated sludge stalled, how advanced o

Ultrafiltration Membrane Selection: Pore Size, Material and the Cleaning Regime Behind Service Life

2026-10-08

Ultrafiltration sits between microfiltration and reverse osmosis, and selecting a membrane means choosing a pore size, a material and a cleaning regime together. This article covers PVDF and PES against PAN, PVC and ceramic alternatives, the construction

Ammonia Nitrogen Measurement: Picking Between Nessler, Salicylate and Electrode Methods

2026-10-08

Ammonia nitrogen can be measured by Nessler colourimetry, the salicylate-hypochlorite method, an ammonia gas-sensing electrode, or distillation followed by titration. This article sets out the detection limits, working wavelengths and interference profile

Stabilization Ponds: Sizing Anaerobic, Facultative and Aerobic Stages as Resource Units

2026-10-08

Stabilization ponds treat wastewater and produce biomass at the same time, which makes them a resource unit as much as a treatment step. This guide sets out how anaerobic, facultative, aerobic and aerated ponds differ, the loading and geometry parameters

Total Phosphorus Monitoring: Digestion, Interferences and the Limits Behind the Standards

2026-10-08

Total phosphorus is measured only after digestion converts every form in the sample to orthophosphate, and most of the error lives in that step. This article covers the national standard ammonium molybdate methods, the digestion options and their practica

Sizing a Biological Contact Oxidation Tank: Filler Choice, BOD Load and Retention Time

2026-10-08

Biological contact oxidation borrows from both biofilm and activated sludge practice, and most of its behaviour comes down to filler selection. This guide covers how pore size is matched to BOD5 and suspended solids, what three-dimensional elastic filler

UASB Reactors: Granular Sludge, the Three-Phase Separator, and Where Designs Actually Fail

2026-10-08

A UASB reactor lives or dies on granular sludge and on the three-phase separator that keeps it inside the vessel. This article works through the reactor internal zones, the biomass concentrations and settling behaviour that define a healthy bed, the three

Anaerobic Digestion in Four Stages: Reading a Reactor Before Methanogenesis Collapses

2026-10-08

Anaerobic treatment is often introduced as a sludge and energy story, but what decides whether a digester holds is the sequence of hydrolysis, acidification, acetogenesis and methanogenesis running in balance. This piece walks through all four stages with