Iwa international Specialist Conference

15.

Influence of sewage fertiliser products on sustainability of farming

Håkan Jönsson, Björn Vinnerås, Pernilla Tidåker

Swedish University of Agricultural Sciences

Background

In a sustainable society, enough food should to be produced both for the present, as well as for the future, probably larger, population. Thus, neither the quantity nor the quality of the crops produced may decrease. Combining this with the principle of caution and with the way agricultural production functions gives five requirements. 1) Neither the concentration nor the availability nor the total mass of plant nutrients may decrease in the agricultural soil, since this may negatively affect the productivity of the soil. 2) The productivity of the arable soil may not be physically hampered, e.g. by soil compaction. 3) To make sure that neither the crop quality nor the soil quality is negatively affected, accumulation of poisonous elements, like heavy metals, must be avoided in the agricultural soil. 4) Likewise, accumulation of xenobiotic substances must be avoided, since there is a risk that these negatively can affect soil microbes, soil animals and/or crop quantity or quality. 5) Products spread on the agricultural soil may not negatively affect the hygienic quality of neither vegetal nor animal food produced.

Requirement 1 implies that the plant nutrients leaving the field with the harvested crop or in any other way, for example by leaching, must be replaced. To avoid depleting fossil resources, the plant nutrients consumed with the food, and delivered with the excreta, need to be recycled to arable land. Requirement 2 means that concentration should be recycled with lightweight machinery and preferably in concentrated products. Requirements 3, 4 and 5 implies that the sewage fertiliser products recycled to arable land must be hygienically safe, and their use may not lead to accumulation of neither poisonous elements nor of xenobiotic substances in the arable soil. In addition to these requirements, it is also necessary that the sewage fertiliser products are safe and easy to handle, otherwise the farmers will not use them. Thereby, it is advantageous if the concentrations and handling properties of the sewage fertiliser products resembles either chemical fertilisers or manure, because farmers have knowledge and experience of and machinery for handling these products.

Results - composition

Household wastewater consists of urine, faecal matter and greywater and the composition of each fraction is widely different from that of the other ones. The urine only contains elements and material that has been metabolised by the body. Therefore, the composition of this fraction reflects the utilised fraction of the food. This means that urine contains large amounts of plant nutrients, e.g. N, P and K, and only small amounts of non-essential heavy metals, e.g. Hg and Cd (Table 1).

The faeces on the other hand consist of both metabolised and non-metabolised material. Therefore, the faeces contain of less nutrients and more non-essential heavy metals. The greywater reflects the use of materials and chemicals in the household and also, via cloths and utensils etc. in society as a whole. Therefore, this fraction contains more heavy metals and less nutrients compared to urine and faeces (Table 1).

Conventional household wastewater consists of a mixture of urine, faeces and greywater. Urine and faeces contributes the larger part of the nutrients, while the greywater mainly contributes with a large volume, diluting the other two fractions, and with heavy metals, polluting the other two fractions. The composition of the greywater is reflected in the sludge produced in the treatment plant.

Table 1. Proposed new Swedish default values for composition of the different fractions of household wastewater per person and year (Vinnerås et al., 2002)

	Unit	Urine	Faeces	Toilet paper	Greywater	Household wastewater
Wet mass	kg	550	51	8,9	36500	37110
Dry mass	kg	21	11	8,5	20	61
BOD7	g	-	-	-	9500	9500
COD	g	-	-	-	19000	19000
N	g	4000	550		500	5050
P	g	365	183		190	738
K	g	1000	365		365	1730
Cu	mg	37	400		2900	3337
Cr	mg	3,7	7,3		365	376
Ni	mg	2,6	27		450	480
Zn	mg	16,4	3900		3650	7566
Pb	mg	0,73	7,3		350	358
Cd	mg	0,25	3,7		15	19
Hg	mg	0,30	3,3		1,5	5,1
Cd/P-ratio	mg/kg	0,7	20,2		78,9	25,7

Results - fertilisation

Several well documented fertiliser experiments with source separated urine indicate, as could be expected, that the nitrogen in source separated urine has a nitrogen effect that is about 10% less than the effect of chemical ammonium nitrate fertilisers. The phosphorous effect of urine seems to be as good as that of chemical fertilisers. So far there are no experiments reported of source-separated faeces, but the fertilising effect of these ought to be similar to that of compost, i.e. weak nitrogen effect, but good phosphorous and potassium effect. Urine and faeces contain essentially all plant nutrients consumed and if the sewage system does not contaminate or dilute the excreta and if they are sanitised before being used as fertilisers, they ought to fulfil requirements 1 through 4, with the reservation that the ecotoxicological risk associated with medical residues so far has not been well investigated. The excreta also resemble manure, and therefore they well fulfil requirement 5, provided that they have not been too diluted by flush water.

Sewage sludge from a conventional sewage treatment, including chemical precipitation of phosphorous, fulfils requirement 1 for phosphorous but neither for potassium nor nitrogen. It also has problems fulfilling requirements 2 and 3, since the extensive use of different chemical substances in society is reflected by the composition of its sludge. Sewage sludge fulfils requirement 5 and, with proper sanitation, it also fulfils requirement 4.

References

Vinnerås B., Palmquist H., Balmér P., Weglin J., Jensen A., Andersson Å. and Jönsson H. (2002). The characteristics of household wastewater and biodegradable solid waste - a proposal for new Swedish norms. Submitted to Urban Water.

16.

Abstract for IWA International Specialist Conference BIOSOLIDS
Reduction of organic MICROPOLLUTANTS in Norwegian sewage sludge DURING THE 90’s
Kjell Terje Nedland, MSc. & Bjarne Paulsrud, MSc.
Aquateam – Norwegian Water Technology Centre AS

P.O.Box 6875 Rodeløkka

N-0504 Oslo

Tel. + 47 22 35 81 00

Fax. + 47 22 35 81 10
In 1989 the Agricultural University of Norway examined the content of 69 organic micropollutants comprising 21 monthly samples from 13 Norwegian WWTPs, including 10 polycyclic aromatic hydrocarbons (PAH), nonylphenol and –etoxylates (NPE), Di-n-butylphthalate (DBP) and Di (2-ethylhexyl) phthalate (DEHP).
In 1996-97 Aquateam carried out a survey of organic micropollutants comprising 5 monthly composite samples from 8 WWTPs (totally 36 samples, one plant participating only one month) for the Norwegian Pollution Control Authority (SFT). The survey focused on variations in the content of the organic micropollutants polychlorinated dibenzodioxins/dibenzo-furanes (dioxins), 7 polychlorinated biphenyls (PCB), 16 PAHs, NPE, DBP, DEHP and linear alkyl benzene sulphonates (LAS) from month to month and from plant to plant. The results were also compared to data from other countries and to results from a similar survey of organic pollutants in Norwegian manure and compost from organic household waste.
A similar survey of that in 1996-97 was carried out in 2001-02 for the same 7 WWTPs that participated every month in 1996-97, and a plant that was not participating in 1996-97. The samples were collected in the same way and from the same months as in 1996-97. The only difference in the surveys was that another laboratory constellation was used in 2001-02 due to a lower price and a better QA/QC than the constellation used in 1996-97.
In figure 1 percentual reduction in median values for the examined parameters are listed (for the two last surveys the data represent seven WWTPs that participated in both surveys). The median content have been reduced by:

Organic micropollutant	Reduction in median value (%) from
	1989 – 2001-02	1996-97 – 2001-02
Dioxins	-	23
PAH	No reduction	59
NPE	87	82
DBP	<68	91
DEHP	52	29

The PCB median is under the detection limit in the last survey, and this limit is for each PCB congener 88% lower than the 1996-97 median. In the 1989 survey all the samples were under the detection limit of 1 mg/kg DS (in the other surveys the detection limit was 0,005 mg/kg DS) Unfortunately we cannot compare the LAS results from 2001-02 with the former results a
s these were analysed with two different methods.

Figure 1. The organic micropollutant content of Norwegian sludge has been considerably reduced from 1996-97 to 2001-02.

The organic micropollutants with highest priority in Norway are dioxins, PCB and PAH. The content of these pollutants in Norwegian sludge is much lower than the limit values proposed by the European Union for a new sludge directive. However, two of the 40 samples did not comply with the proposed EU standard for NPE, one didn’t comply with the proposed standard for DEHP and one didn’t comply with the proposed standard for LAS. Many samples exceeded the Danish cut off values for NPE, DEHP and LAS. The new cut off value for NPE is exceeded by 35 of 40 samples from the Norwegian survey in 2001-02, even though NPE should have been phased out by the industry since 1996.

In Norway the authorities have set no standards for organic micropollutants in sludge. In stead they have made strict regulations for sludge use (tonnes per ha, area types where sludge is allowed (e.g. not grazing land), crops that are allowed etc.). Sludge use in agriculture in Norway is therefore still regarded as safe as long as the regulations are complied with.
The organic micropollutant content in Norwegian sludge vary considerably from month to month at the same WWTP, and often the variations from month to month is larger than the variations from plant to plant. There is no month that has significantly higher values than other months and the values are randomly distributed among the months and plants. This is most probably due to natural variation in the organic micropollutant content in sludge and the uncertainty in sampling, handling of samples and analysing of these parameters. There is therefore a need for many samples of organic micropollutants in sewage sludge from a plant to indicate the concentration level over time.