Number

345-EN

Section

General Section

Use

Abstract

A plant for chicken processing replaced caustic soda (sodium hydroxide) with magnesium hydroxide in the secondary treatment of waters. This reduced corrosion risks, lowered the quantity of alkali used and improved process stability.

Substituted substances

Alternative Substances

Reliability of information

Internet information: data are from an internet document and only a basic and partial evaluation could be performed

Reason substitution

skin/respiratory sensitizing

Hazard Assessment

Substance to be substituted: Sodium hydroxide causes severe skin burns and eye damage according to ECHA C&L Inventory harmonised classification. Alternative substance: Magnesium hydroxide is not included in the harmonised classification and is not listed in the database of substances known to be very high concern.

Description of Substitution

A chicken processing plant generated daily over 7000 tonnes of waste water, heavily polluted with organic matter and ammonia. The waste water treatment included a biological (secondary) stage. Nitrification was done using caustic soda (sodium hydroxide) as pH regulator and alkali source to transform ammonia in nitrates. The facility substituted caustic soda with magnesium hydroxide. Caustic soda is highly corrosive, to humans and materials and it required a legal permit for the US based plant. The magnesium hydroxide alternative provided several advantages, according to the producer: -safer working conditions, -significantly reduced chemical cost and quantities for alkalinity and pH control -improved pH control and stability -improved solids settling in the secondary clarifier.

Case/substitution evaluation

The substitution is easy to implement and reduces risks to personnel and environment related to handling of concentrated caustic soda. Sodium hydroxide is corrosive when concentrated and irritant when more diluted; magnesium hydroxide is irritant. The alternative improves several parameters in waste water treatment and it reduces costs. Magnesium hydroxide improves process stability (according to producer), this is important for a biological water treatment, where variation in pH can disturb the process. Such processes might be even more difficult to set back on the right track, than purely chemical ones. In such situation the resulting effluent may have still too much ammonia and nitrites, making water discharge hazardous. It also impacts the waste management since some part of the activated mud may be deactivated and withdrawn from the process. Magnesium hydroxide also improves filtration reducing the pollution of the water discharge, as inorganic and (adsorbed) organics are concerned. Magnesium in the resulting waste may be harmful for the soil if it has already a magnesium excess and/or a calcium deficit. But the situation could also be that it can rebalance magnesium deficit. Sodium excess in soils is not to be preferred and sodium is not harmless in this case either.

State of implementation

In use

Availability ofAlternative

Alternative available on the market

Producer/Provider

http://www.arieschem.com/

Type of information supplier

Producer / distributor

Contact

http://www.arieschem.com/

Further information

Magnesium hydroxide MSDS from Sigma Aldrich

Publication source: author, company, institute, year

The description is based on the Case History-Magnesium Hydroxide for Biological Treatment of Wastewater. Activated Sludge and Nitrification Processes at a Chicken Processing Plant, published by the producer, Aries Chemicals Inc. on its website.

Publication source

Type of publication and availability

http://www.arieschem.com/case-study/magnesium-hydroxide/

Date, reviewed

November 26, 2021