In brief: It is best practice to dispose of laboratory waste in a controlled manner. For ester preparation activities, the best practice is to store the waste in appropriately labelled bottles for collection by a licenced waste disposal contractor.
Although it is not prohibited in Australia to use a fume cupboard to evaporate waste, we advise against this practice as it introduces untreated waste into the environment.
Preparation and properties of esters
In schools, ester preparation often involves mixing a few drops of an alcohol and a similar amount of a carboxylic acid in a test tube, along with an acid catalyst such as concentrated sulphuric acid, and then heating the mixture in a water bath. The odour of the ester may then be observed by wafting fumes from the test tube or by pouring the mixture onto a small amount of water in a beaker and observing the odour from the ester layer which forms on top of the water.
On a larger scale, after heating the reaction mixture and allowing it to cool, the mixture may then be transferred to a separating funnel and washed with sodium carbonate solution to remove the acid catalyst as well as any unreacted carboxylic acid.
In school ester preparation activities, depending on the length of the carbon chain, the esters produced may be categorised as highly flammable, flammable or combustible. The alcohols used are also flammable and many are irritating to the skin and respiratory system. While esters often have a sweet fruity aroma, the component acids and alcohols can smell very unpleasant. Esters vary in their miscibility with water according to their chain length and structure.
Disposal of esters
We have researched the trade waste acceptance standards in all of the Australian states and territories and consulted directly with five water authorities. In general, the accepted concentrations for organic compounds are very low (e.g., from 1mg/L to 30 mg/L for saturated hydrocarbons). Flammable substances are specifically prohibited from being discharged to the sewerage system, as are water-immiscible liquids. The only carboxylate anion specified by any of the water authorities is acetate, which is accepted at the concentration of 300 mg/L in the ACT.
If the esters are prepared in test tubes, and not washed or added to water, then the entire contents of the test tubes should be transferred to a non-halogenated organic waste bottle and stored for collection by a licenced waste disposal contractor.
If the ester is washed with water or carbonate solution, then the composition of the aqueous layer would depend on the miscibility of the reagents used and ester(s) produced in the activity. In WA and NSW, small amounts of water-miscible organic substances from science laboratories are allowed to be discharged down the sink as long as there is appropriate dilution. In these states, any aqueous layers produced in ester preparation activities could be neutralised and then washed down the sink with lots of water.
We expect that the concentration of these substances in the aqueous layer would exceed the accepted limits in other jurisdictions. Therefore, in these cases, we recommend that the aqueous layer be transferred to a separate waste bottle labelled as ‘Dilute aqueous waste’ and stored for collection via a licenced waste disposal contractor.
Best practice, would be to store the organic layer in a separate bottle to the aqueous layer. However, if the layers are difficult to separate, then it would be reasonable to transfer both layers to the same waste bottle.
Glassware contaminated with any of the organic compounds used or produced can be rinsed with a small amount of ethanol with the rinse liquid being added to the organic waste bottle. If any gas is produced from the stored mixture, it is likely to be carbon dioxide produced from the reaction of the sodium carbonate and the acid catalyst or unreacted carboxylic acid.
It is good practice to keep track of the substances which are added to a waste bottle. One way to do this is to attach a blank label onto the back of the waste bottle. Each time waste is added to the bottle, the names of the substances added can be recorded on the label. When the bottle is full, then the hand-written label can be replaced with a printed label containing this information.
Some schools use gourmet jelly beans to experience the aroma of esters; see the esters experiment alternative, Esters – A tasty investigation http://www.labnetwest.asn.au/resources/experiments/. Do remember to use a non-science room for all activities where foods are consumed.
Agriculture and Resource Management Council of Australia and New Zealand and Australia and New Zealand Environment and Conservation Council, Guidelines for Sewerage Systems, Acceptance of Trade Waste (Industrial Waste), November 1994. http://www.environment.gov.au/resource/guidelines-sewerage-systems-accep...
Water Services Association of Australia, Australian Sewage Quality Management Guidelines, 2012. https://www.wsaa.asn.au/shop/product/5696 (Link updated June 2020)
Water Services Association of Australia, National Wastewater Source Management Guidelines, 2008. https://web.archive.org/web/20090915003859/https://www.wsaa.asn.au/Publications/Documents/WWSM%20Guideline.pdf (Original link replaced with link to Internet Archive June 2020)
Links to information specific to states and territories
ACT Electricity and Water Authority, Acceptance Guideline 1- General Acceptance Criteria for Liquid Waste.
NSW Department of Water and Energy, Liquid Trade Waste Regulation Guidelines, April 2009, http://www.water.nsw.gov.au/ArticleDocuments/36/town_planning_water_util...
NT Power and Water Corporation, Trade Waste Code, http://www.powerwater.com.au/__data/assets/pdf_file/0004/44338/Trade_Was...
Qld, City of Gold Coast, Trade Waste Guidelines: Management of commercial and industrial sewage, effective July 1 2015, http://www.goldcoast.qld.gov.au/trade-waste-guidelines-22798.html
SA Water, Restricted Trade Waste Acceptance Standards, http://www.sawater.com.au/NR/rdonlyres/8E8F6482-D4B4-4AD5-8D75-B2990F4F3...
Tasmania, TasWater, Trade Waste Brochure, http://www.taswater.com.au/ArticleDocuments/318/TasWater%20Trade%20Waste...
Victoria, Barwon Water, Trade Waste Information http://www.barwonwater.vic.gov.au/business/trade-waste
Victoria, City West Water, Trade Waste Information. https://www.citywestwater.com.au/business/trade_waste.aspx
Victoria, Goulburn Valley Water, Trade Waste Information http://www.gvwater.vic.gov.au/business/trade-waste/trade-waste-customers/
Victoria, South East Water, Trade Waste Information http://southeastwater.com.au/Business/TradeWaste/Pages/TradeWaste.aspx
Victoria, Yarra Valley Water, Trade Waste Information http://www.yvw.com.au/Home/Inyourbusiness/Tradewaste/index.htm
WA Water Corporation Acceptance criteria for trade waste – Information Sheet 6 http://www.watercorporation.com.au/~/media/files/business/trade-waste/ap...
WA Water Corporation Laboratory chemical waste – https://www.watercorporation.com.au/home/business/trade-waste/trade-wast...