ISO 16075-6:2023

INTERNATIONAL ISO
STANDARD 16075-6
First edition
2023-12
Guidelines for treated wastewater use
for irrigation projects —
Part 6:
Fertilization
Lignes directrices pour l'utilisation des eaux usées traitées en
irrigation —
Partie 6: Fertilisation
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Source of macronutrients and trace elements in TWW . 2
4.1 General . 2
4.2 Nitrogen (N) . 2
4.3 Phosphorus (P) . 2
4.4 Potassium (K) . 3
4.5 Trace elements . 3
5 Concentration of macronutrients at various levels of wastewater treatment .3
6 Nutrient cycle and reactions in soil .4
6.1 General . 4
6.2 Nitrogen . 4
6.3 Phosphorus . 6
6.4 Potassium . 7
6.5 Micronutrients . 7
7 Fertilizer requirements . 8
7.1 Nutrient requirement by crops . 8
7.2 Soil fertility assessment . 9
8 Calculation of nutrient contribution by TWW . 9
8.1 General . 9
8.2 Nitrogen . 10
8.3 Phosphorus . 10
8.4 Potassium . 11
9 Scheduling of nutrient supply rate by TWW according to crops’ needs .11
9.1 Growth season total nutrient application . 11
9.2 The distribution of nutrient application throughout the irrigation season . 11
10 Adjusting fertilizers for use with TWW .13
11 Combining organic amendments and fertilizers in plots irrigated with TWW .14
12 Monitoring in the context of nutrient value of TWW .14
12.1 Water monitoring . 14
12.1.1 Sampling . 14
12.1.2 Analysis . 16
12.2 Soil . 16
12.2.1 Soil sampling . 16
12.2.2 Frequency of the soil sampling . 17
12.2.3 Sampling procedure . 17
12.2.4 Sample preparation . 17
12.2.5 Soil test methods . 17
12.2.6 Suction cups . 17
12.3 Plants . . 18
12.3.1 General . 18
12.3.2 Frequency of monitoring . . 18
13 Short guide to schedule fertilization in plots irrigated with TWW .18
Bibliography .20
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 282, Water reuse, Subcommittee SC 1,
Treated wastewater reuse for irrigation.
A list of all parts in the ISO 16075 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Treated wastewater (TWW) contains nutrients that are essential for the proper development of various
crops irrigated with it, but can also have a detrimental effect on crops, soil, natural water sources and
the environment in general.
There are several reasons why it is critical to optimize TWW and additional amendments (e.g. manure,
sludge, synthetic fertilizers):
— Using excessive quantities is costly and wasteful.
— Leaching excess nutrients that the crops do not utilize can pollute groundwater and add additional
treatment costs and health risks to drinking water supplies.
— Climate change phenomena that cause drought or storm cycles can overwhelm infiltration capacity
and runoff to pollute streams and waterways.
— Phosphorus excess in diffuse or point source runoff causes eutrophication of water bodies and
upsets the balance in wetlands and other valuable environmental resources.
— Current scientific knowledge, as provided in this document, enables users to balance nutrients and
forecast their impact more accurately to enhance crops and their profitability.
Thus, it is very important to create a plan of the types and amounts of fertilizers that should be added
to various crops, taking into account the amounts of nutrients that already exist in the TWW that is
used to irrigate the crops.
The concentration of nutrients found in TWW depends, among other things, on the source of the
wastewaters and on the level of treatment given to the wastewater, with concentration decreasing at
each stage, in the initial, secondary, tertiary and advanced treatment stages.
The fertilization plans of the various crops should take into consideration the nutritional value found
in TWW, with awareness that, along with the positive contribution of the nutrients in TWW, there are
other aspects that should be considered when developing the fertilization plans, such as:
— the total amount of each nutrient applied during an irrigation season;
— synchronization between nutrient application with TWW irrigation and crop needs;
— availability of nutrients to the crops according to the chemical forms existing in TWW, in comparison
with nutrient availability in inorganic fertilizers.
Understanding all these factors will contribute to reducing or eliminating the negative effects that
excess nutrients can produce on soils, crops, natural water sources and the environment, adjusting or
reducing the amounts of nutrients supplied to the various crops by inorganic fertilizers. The fertilization
programme should also take into account nitrogen and phosphorus from other sources that crops can
use, such as soil or crop residue.
v
INTERNATIONAL STANDARD ISO 16075-6:2023(E)
Guidelines for treated wastewater use for irrigation
projects —
Part 6:
Fertilization
1 Scope
This document provides guidelines for the evaluation of the fertilizer value of treated wastewater
(TWW) at different treatment levels, for an effective fertilization of crops irrigated with TWW. This
document covers:
— evaluation of the nutrient quantities provided by TWW and the synchronization between crop
needs and the nutrients applied with TWW;
— availability of nutrients to crops irrigated with TWW;
— monitoring nutrients in water, soil and crops irrigated with TWW;
— matching between TWW quality and fertilizer properties.
Risk assessment and risk management for the safe use of TWW in irrigation projects are addressed in
[1] [2]
ISO 20426 and ISO 16075-2 .
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 20670, Water reuse — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20670 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
denitrification
reduction of nitrate and/or nitrite to nitrogen or dinitrogen monoxide, usually by the action of bacteria
[3]
[SOURCE: ISO 6107:2021, 3.160 ]
3.2
micronutrients
elements which are required by plants in only very small amounts
Note 1 to entry: Although these are present in plants at very low rates, such macronutrients as nitrogen and
potassium, they are essential for normal plant growth.
3.3
nitrification
oxidation of ammonium compounds by bacteria
Note 1 to entry: Usually the intermediate product is nitrite and the end product nitrate.
[3]
[SOURCE: ISO 6107:2021, 3.359 ]
3.1.4
macronutrients
elements which are required by plants in the largest amount (nitrogen, phosphorus and potassium)
4 Source of macronutrients and trace elements in TWW
4.1 General
Sources of macronutrients and micronutrients in TWW should be evaluated in order to take advantage
of these nutrients in the fertilization programme of the crops, with a view to partially replacing the
fertilizers and avoiding damage that excesses could cause to crops, soils and water resources.
The amount of nitrogen and phosphorus to be supplied to the crop is calculated using the nitrogen and
phosphorus fertilization balance.
4.2 Nitrogen (N)
The main sources of nitrogen in municipal wastewater are faeces (about 20 % of the nitrogen in
municipal wastewater), urine (about 75 % of the nitrogen in municipal wastewater) and food scraps.
These sources contribute between 3,5 kg and 6,9 kg of nitrogen per capita per year (about 40 % as
[4,5]
ammonium and about 60 % as organic nitrogen). In raw wastewater, nitrogen appears mainly as
ammonium and organic nitrogen (soluble or suspended). In the soluble fraction, most of the nitrogen
is found in urea or amino acids and in the suspended fraction – in proteins – and the nitrate-nitrogen
concentration is very low. When the organic load is higher than is common in municipal wastewater,
such as dairy or food industry wastewater, the overall nitrogen concentration can reach much higher
values.
The range of nitrogen concentration in raw municipal wastewater is wide, depending on water use per
−1 −1 −1
capita, from 20 mg l to 70 mg l total nitrogen with a typical concentration of 40 mg l . The organic
−1 −1 −1 -1 [6]
nitrogen is in the range 8 mg l to 25 mg l and the ammonium is in the range 12 mg l to 45 mg l .
However, it should be taken into account that not all the nitrogen forms (such as organic nitrogen)
present in the TWW will be immediately available to the crops.
4.3 Phosphorus (P)
The predominant phosphorus sources in wastewaters are human excretion and detergents. These
[7]
sources contribute, respectively, with 1,5 g and 0,4 g of phosphorus per day per person. Raw
wastewater contains inorganic and organic bound phosphorus.
−1
The range of total phosphorus concentration in raw municipal wastewater is wide, from 4 mg l to
−1 -1 [6]
12 mg l , with a typical concentration of 7 mg l .
Higher concentrations can be observed when the treatment plant receives industrial wastewater and/
or wastewater from animal husbandry.
−1 −1
The inorganic phosphorus content in raw municipal wastewater is in the range 3 mg l to 10 mg l ,
−1 −1
with a typical concentration of 5 mg l ; the organic phosphorus content is in the range 1 mg l to
−1 -1 [6–8]
4 mg l , with a typical concentration of 2 mg l .
However, it should be taken into account that not all the phosphorus forms present in the TWW will be
immediately available to the crops, as they absorb this nutrient in the inorganic form.
4.4 Potassium (K)
Three main sources of potassium in TWW are known. The main source is human urine excreted with
−1 −1
municipal wastewater (20 mg l to 170 mg l of potassium). Other sources are animal excrement
and industrial wastewater in factories where sodium salts have been replaced by potassium in water-
−1
softening systems. The range of potassium content in raw municipal wastewater is wide, from 5 mg l
-1 [9]
to 25 mg l .
4.5 Trace elements
The main sources of trace elements in wastewater are freshwater and any additions from domestic,
industrial and agricultural water use. Trace elements are widely used in industries such as metal
coating, batteries, animal hide processing, the chemical industry, the textile industry and the electronics
industry. Corrosion of water pipes is also a source of trace elements.
The range of trace elements content in raw municipal wastewater is wide, depending on the proportion
of industrial wastewater flowing to the treatment plant.
Some of these trace elements are also essential micronutrients for crops. This document covers the role
of trace elements as micronutrients for crops and not their possible toxic effect on crops or their entry
[10]
into the food chain. These deleterious effects are presented in ISO 16075-1.
The concentration range in TWW for several trace elements is presented in Table 1.
Table 1 — Concentration of trace elements in raw wastewater and removal by wastewater
a
treatment
Removal range according to the level of treatment
Range
(primary to tertiary)
Element
−1
mg l
%
Arsenic (As) < 0,000 3 to 1,9 3 to 52
Boron (B) < 0,123 to 20,0 0 to 13
Cadmium (Cd) < 0,001 2 to 2,1 17 to 84
Chromium (Cr) < 0,000 8 to 83,3 0 to 85
Copper (Cu) < 0,000 1 to 36,5 0 to 84
Lead (Pb) 0,001 to 11,6 0 to 93
Mercury (Hg) < 0,000 1 to 3,0 33
Nickel (Ni) 0,002 to 111,4 0 to 44
Zinc (Zn) < 0,001 to 28,7 6 to 97
NOTE  Values are indicative since wastewater composition can change over time and by location.
a
Modified from References [6] and [11].
5 Concentration of macronutrients at various levels of wastewater treatment
The concentration of nitrogen and phosphorus in TWW decreases according to the treatment level:
primary, secondary, tertiary or any specific treatment to remove N and P. Table 2 presents comparative
data on the concentrations of nitrogen and phosphorus at different treatment levels.
Each stage of treatment reduces nitrogen and phosphorus through the removal of organic matter by
sedimentation or biological treatment. Further removal of nitrogen and phosphorus can be performed
by dedicated treatments.
NOTE Agricultural use of TWW requires storage in order to balance the flows between TWW production
and its consumption. During storage, both elements will decrease, depending on the initial concentrations at
the entrance to the reservoir and the corresponding retention time. The initial concentration depends on the
biological wastewater treatment efficiency, and that is affected by temperature. Thus, the nutrient concentrations
in TWW treated biologically fluctuates seasonally in regions with high temperature variations.
Table 2 shows that TWW with more intensive treatments than activated sludge, such as activated
sludge with biological nutrient removal, activated sludge with biological nutrient removal and filtration
or membrane treatment, contains nutrients at a relatively low concentration. In these cases, TWW's
contribution to the fertilization programme is low to negligible.
a
Table 2 — Typical range of TWW quality after treatment
Activated sludge
Conventional
Raw with biological Membrane
Constituent Unit Primary activated
wastewater nutrient bioreactor
sludge
removal
−1
Ammonia nitrogen mg N l 12 to 45 21 1 to10 1 to 3 1 to 5
−1
Nitrate nitrogen mg N l 0-trace 0,1 10 to 30 2 to 8 < 10
−1
Total nitrogen mg N l 20 to 70 51,6 15 to 35 3 to 8 < 10
−1
Total phosphorus mg P l 4 to 12 5,1 4 to 10 1 to 2 0,3 to 2
a
Modified from Reference [6].
Compared to nitrogen and phosphorus, whose concentration varies according to the level of treatment,
the potassium concentration does not change because conventional wastewater treatment does not
remove salts. Therefore, the concentration will be similar to the concentration in raw wastewater.
Evaluation of the fertilizer value of the TWW should be made based on reservoir water samples, as
explained in 12.1.
6 Nutrient cycle and reactions in soil
6.1 General
The part of the nutrients added with the TWW that will be available for the plants depends on the
reactions of the nutrients in the soil.
6.2 Nitrogen
The nitrogen cycle in the soil is presented in Figure 1.
Figure 1 — Nitrogen cycle in the soil
The total nitrogen content in soil is composed of inorganic and organic compounds.
+ - -
The inorganic forms of soil nitrogen include ammonium (NH ), nitrite (NO ), nitrate (NO ) and
4 2 3
+
gaseous forms (N O; NO; N ). From the point of view of plant nutrition, ammonium (NH ) and nitrate
2 2 4
-
(NO ) are of the greatest importance.
The organic forms of soil nitrogen are present as amino acids, amino sugars and other organic fractions.
Plants absorb the nitrogen in the forms of ammonium and nitrate in a proportion according to the
plant's stage of development, type of plant and soil environment.
A fraction of organic soil nitrogen can be mineralized and become available in ionic forms. Nitrogen
mineralization is the production of inorganic N (generally ammonium) from organic nitrogen. The
[7] [8]
percentage of organic nitrogen in TWW can vary between 10 % and 30 %, with higher values in
TWW of lower treatment levels (see also Table 2).
Ammonium is a monovalent cation partitioned between the soil solution and the exchange complex of
the clay minerals in the soil.
Nitrification is the process of oxidation of ammonium to nitrate. It is a two-step microbial process,
consisting of the conversion of ammonium to nitrite and then further oxidation to nitrate in a process
mediated by aerobic-autotrophic bacteria. The pathway of the nitrification process is presented in
Formulae (1) and (2).
+ - +
NH + 1½ O → NO + H O + 2H (1)
4 2 2 2
- -
NO + ½ O → NO (2)
2 2 3
The soil bacteria responsible for the first oxidation step are mainly Nitrosomonas spp, while Nitrobacter
spp are involved in the second step.
Nitrate ion is not likely to be retained in most soils as a result of its negative charge and weak adsorption
in the soil. Therefore, some can be lost through leaching below the rooting zone and eventually to the
groundwater. Losses can also occur as gas by the denitrification process.
At the moment that TWW nitrogen reaches the soil it becomes part of the soil nitrogen cycle. The
ammonium in the TWW, as well as that derived from organic matter mineralization, is nitrified to
nitrate, at a rate depending on soil characteristics and environmental conditions.
6.3 Phosphorus
The phosphorus cycle in the soil is presented in Figure 2.
Figure 2 — Phosphorus cycle in the soil
Phosphorus is present in soil in both organic and inorganic compounds, the inorganic phosphorus
fractions being higher than the organic phosphorus.
- 2-
Phosphorus is absorbed by the plants as orthophosphate ions (H PO and HPO ) from the soil
2 4 4
solution. The concentration of each ion depends on soil solution pH. At pH 7,2 the two forms are in
- 2-
similar concentration. Below this pH, the main ion is H PO ; at higher pH values the HPO ion is
2 4 4
predominant. Under alkaline conditions, the solubility of phosphorus is low, therefore P is in the form of
salts of low solubility and only a small fraction is found in the soil solution.
3+
Low soluble phosphorus compounds are formed by precipitation. At low pH they are formed with Fe
3+ 2+
and Al ; at higher than pH 7 they are formed with Ca . Phosphorus is also adsorbed to clay minerals in
the soil by different sorption reactions. These various phosphorus forms and their reactions maintain
an equilibrium with the soil solution, from which the plant absorbs phosphorus.
The phosphorus added during TWW irrigation becomes an integral part of the phosphorus cycle
in the soil, contributing organic phosphorus to the pool of fresh organic phosphorus, which after
decomposition of the organic matter releases phosphorus as inorganic phosphorus in the soil. The
inorganic phosphorus added by the TWW is incorporated into the soil solution and reacts as described
previously, either precipitated or adsorbed.
6.4 Potassium
The potassium cycle in the soil is presented in Figure 3.
Figure 3 — Potassium cycle in the soil
Potassium in soil can be classified into three fractions: potassium as a structural element in soil
+ +
minerals, K interchangeable adsorbed to soil colloids (clays and organic matter) and K present in soil
solution.
+ +
The proportion of K in the soil solution is small relative to K in the other fractions. Adsorbed potassium
can be released into solution, as well as potassium in minerals by the weathering process.
+ +
The K applied by irrigation with TWW is dissolved and is in the ionic form. The K added in TWW
+
irrigation becomes an integral part of the K cycle in the soil, is incorporated into the soil solution and
reacts as described previously, being adsorbed.
6.5 Micronutrients
The possible pathways of micronutrients in soil are presented in Figure 4.
a
Modified from Reference [11].
a
Figure 4 — Possible pathways of trace element in soil
The main mechanisms that immobilize dissolved trace elements within the soil appear to be adsorption
and precipitation. Factors that affect the retention of trace elements by soils include soil texture, soil pH,
[8]
soil organic matter and contents of amorphous oxides of Fe, Al and Mn. The soil pH is a determinative
factor for trace element solubility in soils and in the absorption (uptake) of these by the plant.
Trace elements are found in TWW both in the suspended and dissolved solids. Suspended solids
can accumulate on the soil surface and the dissolved trace elements penetrate into the soil. Tillage
[8]
operations tend to homogenize the elements from both fractions in the tilled soil.
A benefit of using TWW for irrigation can be the addition of elements which can correct micronutrient
[7]
deficiencies in high pH and calcareous soils. Accumulation of excessive levels of trace elements can
be a concern, as it could lead to plant toxicity and hence to health and environmental hazards. The
[10]
potential negative effects of trace elements are presented in ISO 16075-1.
7 Fertilizer requirements
7.1 Nutrient requirement by crops
Developing a fertilization programme starts with understanding the crop's nutrient needs in its
different growth stages. Each crop requires different amount of nutrients according to the plant
characteristics, the expected crop production and environmental considerations.
Some examples o
...