Aregger Chemie AG

Phosphates and fish mortality

Karin Jäggi — Tue, 30 Jul 2024 11:44:36 +0000

Phosphates and fish mortality

The phosphorus in our waters must be removed from the water in order to inhibit plant growth (algae). During their growth, algae are useful as suppliers of oxygen. But when they die, sink to the bottom of the lake and decompose, they need a lot of oxygen. This is extracted from the water. This initially kills the fish. At a later stage, the water becomes cloudy due to a lack of oxygen and starts to smell bad.

Before the water is returned to nature, phosphorus must be eliminated in order to promote oxygenation of the water, allow fish to thrive and achieve good water quality.

Process for phosphate elimination

In principle, phosphates could be removed from the water biologically by cultivating phosphorus-consuming flora and skimming or filtering it off as soon as it has done its job. However, this requires large tanks and the process has proven to be unstable in practice. Removing the phosphates chemically is both environmentally friendly and reliable. A chemical substance (precipitant) is dosed into the wastewater treatment plants or sewage treatment plants, which forms an insoluble precipitate with the phosphate. This mixes with the other solids in the wastewater and can thus be removed. Proven precipitants are water-soluble salts of iron or aluminium. Both elements also occur in nature.

Precipitation, flocculation and filtration

Karin Jäggi — Tue, 30 Jul 2024 11:39:10 +0000

Precipitation, flocculation and filtration

In the third wastewater treatment stage, the contaminated water is treated by precipitation with iron salts, hydrated lime and a flocculant. This stage primarily removes sediment and suspended solids, dissolved inorganic substances and those substances from the wastewater that are difficult or impossible to break down biologically. This also includes a number of colourants.

Felling

In precipitation, substances dissolved in water are converted into a completely or partially insoluble state by precipitants. Precipitation is used to separate metal ions, sulphides and phosphates as well as for softening. The precipitation product – in colloidal form – is converted into a separable form by flocculation.

Precipitation takes place in the wastewater treatment plant in so-called reaction tanks and is a chemical process that converts dissolved compounds into an undissolved state by adding suitable chemicals – such as iron and aluminium salts.

In the presence of complexing agents (inorganic or organic compounds that bind metal ions), sulphide precipitation may be necessary. Interfering anions are precipitated in the form of their salts (calcium, iron or aluminium salts).

Flocculation

The initial phase of flocculation is coagulation. In order for the finely dispersed colloids to be separated effectively, it is necessary to form the largest possible flocs from the small particles. Floc formation is favoured by the addition of mineral, organic, artificial or natural flocculants.

Most of the particles (colloids) remaining after precipitation are so small that they cannot be filtered. By adding a coagulant (e.g. ferric chloride, aluminium sulphate, calcium hydroxide) and then adding a flocculant (e.g. polyelectrolyte PE), flocs are formed under defined pH conditions. The large flocs enable solid-liquid separation by sedimentation (sedimentation tank, lamella separator) or filtration (pebble filter with backwash).

Filtration

The flocs are removed from the water using suitable physical processes such as sedimentation, filtration or flotation.

Source:
Federal Office for the Environment, Fact sheets on water and exhaust air treatment processes, dated 28 March 2017, p. 10 (slightly abridged)

Waste water treatment in sewage treatment plants

Karin Jäggi — Tue, 30 Jul 2024 11:32:21 +0000

Waste water treatment in sewage treatment plants

The aim of wastewater treatment is to remove the pollutants. Wastewater treatment plants (WWTPs) in Switzerland purify wastewater in three to five stages.

Mechanical treatment stage (screen, grit chamber and primary clarifier) to remove solids from the wastewater.
Biological treatment stage in which microorganisms break down pollutants in the wastewater and convert toxic nitrogen compounds into more harmless nitrate.
Third treatment stage, which removes phosphorus from the wastewater by adding chemicals.

Sand and activated carbon filters and/or ozone are also often used.

We offer you a complete range of products for the third treatment stage and comprehensive advice on increasing the performance of your wastewater treatment plant.

Water and waste water

Karin Jäggi — Tue, 30 Jul 2024 11:25:51 +0000

Water and waste water

Raw water and drinking water

In Switzerland, a distinction is made between raw water (untreated surface water or groundwater) and drinking water. The regulations for untreated water in Switzerland can be found in the Federal Act on the Protection of Waters (Waters Protection Act, SR 814.20) and the associated ordinance, as well as in cantonal regulations.

Drinking water, on the other hand, is regulated by the Federal Act on Foodstuffs and Utility Articles (Foodstuffs Act, SR 817.0) and the Foodstuffs Ordinance. Drinking or tap water is the most closely monitored foodstuff in Switzerland and fulfils the highest standards of hygiene and safety. It is constantly subject to strict controls and is of very high quality.

Waste water

Wastewater consists to a large extent of water and pollutants, which occur in dissolved and undissolved form as well as organic compounds (fats, proteins, carbohydrates). Wastewater is a generic term and comes from various sources (e.g. from rainwater, external water or wastewater such as grey or black water).

Wastewater contains biodegradable nutrients (e.g. glucose), nutrients (e.g. nitrogen and phosphorus compounds), pollutants (synthetic and organic substances, toxins, microplastics, etc.) and impurities (salts, fats, sand).

Different wastewater treatment processes are required depending on the composition of the wastewater. In Switzerland, wastewater must be channelled into sewage treatment plants via the sewage system for disposal. It is then channelled into receiving waters or groundwater.