🌿 Kjeldahl nitrogen in sewage sludge, treated biowaste and soil — portion of 0.2–1 g of dried sample (or a moist or liquid sample with the corresponding dry matter), 10 ml sulfuric acid and 2.5 g of K2SO4:CuSO4:TiO2 10:1:1 catalyst, digestion in a block at up to 400 °C, distillation of ammonia after adding NaOH into boric acid and titration with sulfuric or hydrochloric acid; nitrate and nitrite are not included in the result, LOD usually 0.03 % N, LOQ 0.1 % N, PN-EN 16169

Environment PN-EN 16169

Overview

WHAT THE STANDARD COVERS. The scope on the PKN catalogue card of PN-EN 16169:2012 (English version) (our translation): “Specifies a method for the determination of Kjeldahl nitrogen according to the Kjeldahl procedure in sewage sludge, treated biowaste and soils. The method does not include nitrate and nitrite. Nitrogen compounds with N-N, N-O bonds and some heterocyclic compounds (pyridines) are only partially determined. NOTE The typical LOQ is 0.1 % N; the typical LOD is 0.03 % N (using 0.25 N sulfuric acid for titration)”. We read the text of the standard in the iTeh sample of SIST EN 16169:2013 (text of EN 16169:2012, English): from the title page through the contents, foreword, introduction and Clauses 1–8 up to and including the beginning of the digestion in 9.2 (addition of the catalyst). Outside the sample remain the rest of 9.2 (heating programme), 9.3–9.5 (titration, performance check, blank test), Clauses 10–13 (calculation, expression of results, precision, test report) and Annex A.

ACCORDING TO THE TEXT OF EN 16169:2012 (introduction, Clauses 1–8, beginning of 9.2). The standard was prepared by CEN/TC 400 “Horizontal standards in the fields of sludge, biowaste and soil” (secretariat DIN) under European Commission mandate M/330; CEN approved it on 24.05.2012. Validation (Table 1): municipal sludge, fresh compost and compost, sludge-amended soil and agricultural soil. Scope (1): Kjeldahl nitrogen according to the Kjeldahl procedure in sewage sludge, treated biowaste and soil; nitrate and nitrite are not included; compounds with nitrogen in N–N and N–O bonds and some heterocycles (pyridines) are only partially determined; limit of detection usually 0.03 % nitrogen, limit of quantification 0.1 % nitrogen (with titration using sulfuric acid 0.25 mol/l). Normative references (2): EN 15934 (dry matter), EN 16179 (sample pretreatment), EN ISO 3696, EN ISO 5667-15 (storage of sludges), ISO 18512 (storage of soil). Definition (3.1, after EN 13342:2000): nitrogen contributed by free ammonia, inorganic ammonium compounds and those organic nitrogen compounds that the described digestion (catalytic, with sulfuric acid) converts to ammonium sulfate. Principle (4): dried and homogenised, moist or liquid material is digested in a Kjeldahl tube with sulfuric acid; the addition of potassium sulfate raises the temperature, the catalyst is e.g. a mixture of titanium dioxide and copper sulfate; after adding sodium hydroxide, ammonia is distilled off, condensed and collected in boric acid solution (or diluted sulfuric acid), then titrated with sulfuric or hydrochloric acid. Sources of error (5): nitrogen from N–N and N–O bonds (e.g. azo, nitro and nitroso compounds, hydrazines, hydrazones, oximes, pyrazolones, isoxazoles, diazines and triazines) is not completely recorded; the inorganic fraction (nitrate and nitrite) is not determined; contamination of the apparatus — rinsing after each series and blank determinations; the amount of sulfuric acid depends on the composition of the sample (Table 2: consumption of acid 36 mol/l in ml per gram — soil organic carbon 10.0, soil organic matter 5.8, Al2O3 1.63, Fe2O3 1.04, clay 0.60, CaCO3 0.55, silt 0.33, sand 0, salicylic acid 6.76, Na2S2O3 0.58, reduced iron 1.50); for samples rich in organic matter a sample to acid ratio of at least 1:10 (mass to volume); block temperature not above 400 °C to avoid loss of analyte. Reagents (6): water of grade 2 according to EN ISO 3696; sulfuric acid ρ = 1.84 g/ml; catalyst mixture — 200 g K2SO4, 20 g CuSO4·5H2O and 20 g TiO2 in the anatase form, ground and mixed (10:1:1), also commercially available; sodium hydroxide 10 mol/l; boric acid solution 20 g/l; mixed indicator — 0.1 g bromocresol green and 0.02 g methyl red in 100 ml ethanol; sulfuric or hydrochloric acid c(H+) = 0.01–0.50 mol/l. Apparatus (7): Kjeldahl flasks or tubes, a block for digestion with sulfuric acid at a temperature close to 400 °C, a distillation apparatus e.g. of the Parnas–Wagner type or another with a steam generator. Samples (8): soil is stored according to ISO 18512, sludges according to EN ISO 5667-15, biowaste — like soil; pretreatment according to EN 16179; results are referred to dry matter, so for moist and liquid samples the dry matter is determined on a separate portion according to EN 15934. Digestion (9.2, beginning): a portion of about 0.2–1 g of dried sample or an undried sample with the corresponding dry matter, weighed to 0.1 %; larger portions are possible — the mass is chosen according to the nitrogen content; for the semi-micro and macro variants — flasks or tubes of suitable volume; 10 ml sulfuric acid (note 1: the amount may be adapted to the size of the vessel); swirl until the sample is fully wetted, leave to cool, add 2.5 g of the catalyst mixture.

STATUS (card as of 03.10.2026). The PKN card of PN-EN 16169:2012 (English version, published 22-10-2012, 12 pages, price group F) has no “Withdrawn” header: Health, Environment and Medicine Sector, KT 121 Water Quality — Chemical Testing — Inorganic Substances, ICS 13.030.01 and 13.080.10, “Introduces: EN 16169:2012 [IDT]”; the card has no “Replaces” or “Replaced by” fields. There is no Polish language version in the PKN search (term “PN-EN 16169”, 03.10.2026). In the iTeh catalogue (read on 03.10.2026) EN 16169:2012 has the status “Published”, stage 90.93 “Decision to confirm” (review from 11.07.2024, completed on 30.09.2026), committee CEN/TC 444, and a link to Directive 86/278/EEC (protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture). Kjeldahl nitrogen in sewage sludge alone is also described by the older standard PN-EN 13342 (separate entry “Kjeldahl nitrogen in sewage sludge — mineralisation with sulfuric acid with a catalyst, distillation and determination of the ammonia”), from which definition 3.1 is taken.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read on 03.10.2026). The number 16169 appears in 5 records at 4 laboratories: AB 415, AB 447, AB 1095, AB 1768. In the current PCA documents (read on 03.10.2026, issues from 27.11.2025 to 16.07.2026) the number appears in 5 items of the same 4 laboratories (AB 1095 — 2, the others 1 each). The form is “PN-EN 16169:2012” everywhere and always as the only reference document in the item; at AB 1095 with the location mark “M”. None of these items is suspended. The “Laboratories” tab (“PN-EN 16169”) shows the same 4 laboratories — checked with the tab query on the production server labcoda.pl on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). Titrimetric method everywhere. AB 415 — sewage sludge, “Sum of ammonium and amine nitrogen content (Kjeldahl nitrogen)” (0.50–10.0) %; the same laboratory has in the adjacent item “Kjeldahl nitrogen content” (0.50–10.0) % according to PN-EN 13342:2002 and ammonium nitrogen according to PN-EN 14671:2007. AB 447 — sewage sludge and waste with code 19 08 05, Kjeldahl nitrogen (0.10–8.0) %. AB 1768 — sewage sludge, Kjeldahl nitrogen (0.50–10.0) %, next to ammonium nitrogen according to PN-EN 14671:2007 and PN-ISO 5664:2002. AB 1095 — two items (0.10–10) %: soil, ground and sewage sludge under the name “Total nitrogen content” and organic, natural and mineral fertilisers and plant cultivation aids (soil improvers, growth stimulants, growing media) under the name “Kjeldahl nitrogen content”; in the latter item there is a separate “total nitrogen” according to the in-house procedure PB-302/LF. Fertilisers, growth stimulants and growing media lie outside the scope of the standard (sewage sludge, treated biowaste, soil).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With the name of the result: Kjeldahl nitrogen is not total nitrogen — nitrate and nitrite are not included (1, 5), so the AB 1095 item named “Total nitrogen content” with this standard gives a result without nitrate and nitrite nitrogen. With the sample: nitrogen from N–N and N–O bonds and from some heterocycles comes out too low without any signal (5). With the acid: a sample rich in organic matter consumes a lot of acid (Table 2) — too little acid (ratio below 1:10) means incomplete digestion; too hot a block (above 400 °C) means loss of nitrogen (5). With dry matter: the result refers to dry matter, and for a moist or liquid sample the dry matter comes from a separate portion (8) — an error in dry matter is carried directly into the result. With the apparatus: a contaminated distillation apparatus raises the result — rinsing after each series and blanks (5). When comparing two standards: at AB 415 the same sludge has an item for Kjeldahl nitrogen according to PN-EN 13342 and according to PN-EN 16169 — the report must show according to which standard the result was given.

WHAT WE DO NOT GIVE. We did not read the rest of the digestion (heating temperatures and times), the titration, performance check, blank test, the calculation formula, the expression of results, the precision data or Annex A, so we do not give them. Nor do we give the requirements of regulations on the use of sewage sludge — we did not read the text of Directive 86/278/EEC or Polish acts for this entry.

Method principle

A portion of sludge, biowaste or soil (usually 0.2–1 g dry matter) is digested in a Kjeldahl tube with 10 ml of concentrated sulfuric acid and 2.5 g of K2SO4:CuSO4:TiO2 (10:1:1) mixture in a heating block, not above 400 °C — ammonium nitrogen and most organic nitrogen are converted to ammonium sulfate. After alkalisation with sodium hydroxide, ammonia is distilled (e.g. with a Parnas–Wagner apparatus or with a steam generator) into boric acid and titrated with sulfuric or hydrochloric acid against a mixed indicator. Nitrate and nitrite are not included in the result; the result refers to dry matter.

Applications

• Sewage sludge, treated biowaste (compost) and soil — Kjeldahl nitrogen (1, Table 1)
• Without nitrate and nitrite; nitrogen from N–N and N–O bonds and from some heterocycles recorded only partially (1, 5)
• Sewage sludge, waste with code 19 08 05, soil, ground, and also fertilisers and plant cultivation aids — titrimetric method in the accreditation scopes of 4 laboratories in PCA

Key parameters

Standard

Standard number

PN-EN 16169:2012

Title (PL)

Osady ściekowe, uzdatnione bioodpady oraz gleba — Oznaczanie azotu metodą Kjeldahla

Title (EN)

Sludge, treated biowaste and soil — Determination of Kjeldahl nitrogen

Step-by-step procedure

1. Sample

   Storage according to ISO 18512 (soil, biowaste) or EN ISO 5667-15 (sludges), pretreatment according to EN 16179; dry matter according to EN 15934. PN-EN 16169:2012 current (PKN card as of 03.10.2026).

2. Portion and acid

   About 0.2–1 g of dried sample (or undried with the corresponding dry matter) into a Kjeldahl tube; 10 ml H2SO4, swirl, leave to cool.

3. Catalyst and digestion

   2.5 g of the 10:1:1 mixture; digestion in a block not above 400 °C — we do not give the further heating programme.

4. Distillation

   After adding NaOH, ammonia is distilled into boric acid (or diluted H2SO4).

5. Titration and result

   Titration with sulfuric or hydrochloric acid; result in % N on dry matter — we do not give the calculation formula. Rinse the apparatus after each series, carry out blanks.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Concentrated sulfuric acid at a temperature close to 400 °C — work in a fume hood
• Sodium hydroxide 10 mol/l is strongly corrosive; adding it to the acidic digest causes strong heating
• The standard warns that it does not address all hazards and that tests are to be carried out by suitably trained staff (introduction)

Frequently asked questions