BS EN ISO 5815-1:2019 pdf – Water quality – Determination of biochemical oxygen demand after n days (BODn) Part 1: Dilution and seeding method with allylthiourea addition (ISO 5815-1:2019).
1 Scope This document specifies the determination of the biochemical oxygen demand of waters by dilution and seeding with suppression of nitrification after 5 d or 7 d incubation time. It is applicable to all waters having biochemical oxygen demands usually between 1 mg/l and 6 000 mg/l. It applies particularly to waste waters but also suits for the analysis of natural waters. For biochemical oxygen demands greater than 6 000 mg/l of oxygen, the method is still applicable, but special care is needed taking into consideration the representativeness of subsampling for preparation of the dilution steps. The results obtained are the product of a combination of biochemical and chemical reactions in presence of living matter which behaves only with occasional reproducibility. The results do not have the rigorous and unambiguous character of those resulting from, for example, a single, well-defined, chemical process. Nevertheless, the results provide an indication from which the quality of waters can be estimated. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3696, Water for analytical laboratory use — Specification and test methods ISO 5667-3, Water quality — Preservation and handling of water samples ISO 5813, Water quality — Determination of dissolved oxygen — Iodometric method ISO 5814, Water quality — Determination of dissolved oxygen — Electrochemical probe method ISO 6060, Water quality — Determination of the chemical oxygen demand ISO 8245, Water quality — Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC) ISO 8467, Water quality — Determination of permanganate index
3.8 free chlorine chlorine present in the form of hypochlorous acid, hypochlorite ion or dissolved elemental chlorine [SOURCE: ISO 7393-1:1985, 2.1] 3.9 combined chlorine fraction of total chlorine present in the form of chloramines and organic chloramines [SOURCE: ISO 7393-1:1985, 2.2] 3.10 nitrification oxidation of ammonium salts by bacteria where usually the intermediate product is nitrite and the end product nitrate [SOURCE: ISO 11733:2004, 3.9] 4 Principle The BOD n , with inhibition of nitrification is determined, using the dilution method. A batch series with different dilutions of a sample is prepared and examined. The dilution water is enriched with oxygen and seeded with adapted aerobic microorganisms. The sample is incubated at (20 ± 1) °C for a specified period (n), 5 d or 7 d, in the dark, in a completely filled and stoppered bottle. The dissolved oxygen concentration is determined before and after incubation. The mass of consumed oxygen per litre sample is calculated. 5 Reagents Use only reagents with the degree of purity “for analysis”. 5.1 Water, at least grade 3 in accordance with ISO 3696. The water shall not contain more than 0,01 mg/l of copper, nor chlorine or chloramines. 5.2 Seeding water, which can be obtained in one of the following ways: a) municipal waste water, decanted or coarsely filtered; b) surface water containing municipal waste water; c) settled effluent from a waste water treatment plant; d) water taken downstream from the discharge of the water to be analysed, or water containing microorganisms that are adapted to the water to be analysed; e) commercially available seeding material.
5.3.5 Iron (III)‑chloride‑hexahydrate solution, ρ = 0,25 g/l. Dissolve 0,25 g of iron (III)-chloride-hexahydrate (FeCl 3 ⋅6H 2 O), in water (5.1). Dilute with water (5.1) to 1 000 ml and mix. 5.4 Dilution water Determine the total volume of dilution water required for the actual test. Pour about half the required volume of water (5.1) into the feed vessel (6.3) for the dilution water and add 1 ml of each of the salt solutions (5.3.2, 5.3.3, 5.3.4 and 5.3.5) for each litre of the total volume. Then fill to the required total volume with water (5.1) and mix by stirring, aeration or shaking. Bring the dilution water obtained in this way to a temperature of (20 ± 2) °C, keep at this temperature and aerate slightly by mixing. If, for example, specially adapted seeding water or seeding material is necessary, the procedure according to Annex C can be followed. EXAMPLE If 20 l of dilution water are required, prepare 10 l of water (5.1). Stirring continuously, add 20 ml of each of the salt solutions individually and fill up with water (5.1) to 20 l. 5.5 Seeded dilution water The preparation of a seeded dilution water is needed when the test solutions are prepared according to 9.3 The mass concentration of oxygen consumed over 5 d (or 7 d) at (20 ± 1) °C by the seeded dilution water with the addition of allylthiourea (ATU) solution to inhibit nitrification [blank value (see 9.5)], shall be between 0,2 mg/l and 1,5 mg/l. The volume increase of the dilution water by seeding water should be as low as possible.