Methodology for the quantification of greenhouse gas emissions during land application of sewage sludge

Figures & data

Figure 1. Sludge management with the most common treatment process ‘E’ is the energy required for the process (generated from fossil fuels).

Table 1. Percentage of wastewater sludge by various disposal methods.

Region	Year	Land application (%)	Incineration (%)	Land-filling(%)	Compost ^a(%)	Others (%)	Ref.^a
USA	–	52.0	22.0	17.0	9.0	–	[1]
Canada		43.0	47.0	4.0		6.0	[2]
Western Canada	–	66.0	–	4.0	27.0	–	[1]
Japan	–	–	80.0	–	–	–	[1]
China	2010	48.5	3.5	34.5	–	13.5	[3]
Australia	2011	55.0	15	30.0	15.0	–	[4]
France	2008	60.0	–	–	–	–	[5]
UK	2005	69.0	14.0	5.0	1	9.0	[6]
Denmark	2007	59.0	16.0	6.0	–	19.0	[5]
Sweden	2009	24.0	1.0	24.0	33.0	18.0	[5]
Germany	2008	28.0	51.0	–	17.5	3.5	[5]
Italy	2005	23.0	3.0	42.0	21.0	11.0	[5]
Belgium	2008	14.0	53.5	–	–	32.5	[5]
Netherlands	2006	–	67.0	4.5	13.0	15.5	[5]
Greece	2008	1.0	46.0	38.0	–	15.0	[5]

^a[1] = LeBlanc et al. (2008); [2] = Roy, Dutta, Corscadden, Havard, and Dickie (2011); [3] = Chen, Yan, Ye, Meng, and Zhu (2012); [4] = http://www.biosolids.com.au/benefits-land-application.php; [5] = Kelessidis and Stasinakis (2012) and [6] = Maisonnave, Montrejaud-Vignoles, Bonni, and Ensct, (2002); Compost is mainly applied to agriculture land or used for horticulture. Other applications: used in cement industry, bricks, etc.

Table 2. Nitrogen and phosphorus contents of sewage sludge.

Type of sludge	Nitrogen content	Phosphorus content	Reference
Sewage sludge	NA	1.2–9.5%	Furrer, Gupta, and Stauffer (1984)
Secondary sludge	3.8%	2.2%	Smith (1996)
Fermented sludge	3.9% (average)	2.5% (average)	Sommers (1977)
Anaerobic sludge	32–96 g N/kg dry mass	24–47 g P2O5/kg dry matter	Johannesson (1999)
Anaerobic sludge	15 g N/kg dry matter	78 g P2O5/kg dry matter	Quilbé et al.(2005)
Thermally stabilized sewage sludge	19 g N/kg dry matter	22 g P2O5/kg dry matter
Aerobic sludge	48 g N/kg dry matter	25 g P/kg dry matter	Sigua, Adjei, and Rechcigl (2005)
anaerobic sludge	40 g N/kg dry matter (pH 11; calcium hydroxide treated)	22 g P/kg dry matter
Cake biosolids	39 g N/kg dry matter	33 g P/kg dry matter
Secondary sludge	21–50 g N/kg dry matter	16–31 g P/kg dry matter	Fernandes, Bettiol, and Cerri (2005a)
Sewage sludge	2.3%	1.1%	Wang et al. (2008b)
Sewage sludge	7 mg TN/kg dry matter	17 g TP/kg dry matter	Wang, Chen, Ge, and Jia (2008c)
Sewage sludge	2.8–5.1%	0.8–3.0%	Chan (2009)
Sewage sludge	30 g TN/kg dry matter	10 g P/kg dry matter	Franco et al. (2010)
Sewage sludge	2.3%	0.4%	Keskin, Bozkurt, and Akdeniz (2010)
Sewage sludge	47 g N/kg dry matter	<1 g P2O5/kg dry matter	Lakhdar et al. (2010)
Sewage sludge	1.4%	0.8%	Kabir, Kamal, Jahan, Faizullah, and Ullah (2012)

Note: NA, not applicable.

Table 3. Description of methods used to estimate GHG emissions due to sludge land application.

Method	Gases included	Parameters used	Limitations of the methods
IPCC	CO2 emissions from vehicles used for transport and during land application of sewage sludge		This method does not account for any benefits of land application of sewage sludge (IPCC, fourth Assessment Report by Bonger et al., 2009). Increase in the flux of gases (CO2, CH4 and N2O; Fernandes et al., 2005b) following the land application are not considered. Emissions reduction resulting from offsetting fertilizer use is not considered
	CH4 and N2O emissions following sludge land application	10.0% of CH4 potential or 5 kg CH4/Mg raw dry solids
	Indirect N2O emissions	1.0% of total nitrogen applied
		Indirect N2O emissions = application rate (kg N applied) × FracGASM × EF4
		Where FracGASM is the fraction of the added N that will volatilize (default value is 0.20) and EF4 is a conversion factor (default value is 0.01) for the fraction of N that volatilizes what will convert to N2O
Research triangular institute (RTI)	CO2 emissions following land application of sewage sludge. The emissions will be directly proportional to the carbon application rate to the land	GHGs emissions = Mg CO2/year, The MW = annual mass of waste applied to the land treatment unit (Mg/yr, wet basis), TSW = total solids content of waste material applied to the land (kg dry solids/kg wet solids), CCw = carbon content of sewage sludge applied to the land (kg C/kg dry solids), 44 = molecular weight of CO2 (kg/kg-mol), 12 = molecular weight of carbon (kg/kg-mol)	This process gives an overestimation of CO2 emissions, as it presumes the complete conversion of carbon content of sewage sludge to CO2. Following the land application, carbon will be converted into CO2 and CH4 due to the presence of anaerobic pockets within the land. Increased in the flux of gases (CO2, CH4 and N2O; Fernandes et al., 2005b) following the land application of sewage sludge are not considered. Emissions reduction resulting from offsetting fertilizer use was not considered
BEAM (Sylvis, 2009)	CO2 emissions from vehicles used for transport and during land application of sewage sludge		CO2 emissions from land due to biosolids application are considered as biogenic sources and they are not included in GHG estimation. CH4 emissions are considered negligible (Ball, Ball, McTaggart, & Scott, 2004; Jones et al., 2006). Increased in the flux of gases (CO2, CH4 and N2O; Fernandes et al., 2005b) following the land application are not considered
	CO2 emissions reductions from carbon sequestration in soil (credit) are considered	CO2eq sequestered (–Mg/day) = dry sludge mass (Mg/day) * estimated CO2 equivalent sequestered (Mg CO2eq/dry Mg sludge; default value = 0.25).
	CO2 emissions reduction resulting from the offsetting fertilizer use.	Replaces commercial nitrogen (N) fertilizer: CO2 equivalent reduction (–Mg/day) = dry biosolids mass (Mg/day) *% total N (default = 4.0%) * N fertilizer credit (–Mg CO2eq/Mg N; default value = 4.00) (Recycled Organics Unit, 2006)
		Replaces commercial phosphorus (P) fertilizer: CO2 equivalent reduction (–Mg/day) = dry sludge mass (Mg/day) *% total P (default = 1.5%) * P fertilizer credit (–Mg CO2eq/Mg P; default = 2.00) (Recycled Organics Unit, 2006)
	N2O emissions following land application of sludge.	N2O emissions (Mg/day) = biosolids applied (dry Mg/day) *% N in biosolids *% of biosolids applied to fine textured soils *% of N that goes to N2O
		% of N that goes to N2O
		For fine textured soils = 2.3%
		For coarse textured soils = 0.05%
		For fine and coarse-textured soils (factor for N conversion to N2O)
		C/N > 30, N conversion to N2O factor is 0
		C/N < 30, N conversion to N2O factor is 1.57
		C/N in the biosolids
Lundin et al. (2004)	Positive benefits of nitrogen and phosphorous (18 kg of phosphrous/Mg of dry solids) are considered. N2O and NO3 are likely to be released when the organically bound nitrogen in sludge is mineralized	GHG emission factors (kg/Mg of dry solids)  CO2  CH4 N2O  25.00 −0.01 −0.19	CH4 and CO2 emissions due to sludge land application are not described. An increase in the flux of gases (CO2, CH4 and N2O; Fernandes et al., 2005b) following the land application are not considered. The negative value was not defined by the authors
Hospido, Moreira, Martín, Rigola, and Feijoo (2005)	Benefits of nitrogen 17.87 kg N/Mg of dry solids and phosphrous 14.32 kg P/Mg of dry solids) due to sludge application was considered	CO2  CH4  N2O  NA  3.18  NA	There was no explanation for the values utilized for evaluating the GHG emissions. The authors did not consider (avoided) CO2 and N2O emissions from the land application of sludge
Hong, Hong, Otaki, and Jolliet (2009)	Positive benefits of nitrogen are considered. The other factors are taken from inventory data without proper explanation	CO2  CH4  N2O 17.20 −21.30 −0.19	The authors have not considered carbon sequestration due to land application of sludge. Moreover, authors have not included increased flux of gases at the soil–atmosphere interface due to the land application of sludge. Compare to Lundin et al. (2004) and Hospido et al. (2005) the methane emission factor was different. The representation of negative sign was not mentioned
Niu, Huang, Dai, and Zhao (2013)	Positive benefits of the nitrogen content present in sludge was considered. Further explanation of the factors was detailed	CO2  CH4  N2O 17.2  3.18  NA	Authors have considered CO2 emissions values from Hospido et al. (2005) and CH4 factor from Hong et al. (2009) but they have not included N2O emissions. There was no explanation behind the assumption considered in computing GHG emissions
This study	• CO2, CH4 & N2O emissions and reductions are considered	Details of these parameters used are explained in Section 4. The parameter (or factors) considered in evaluating GHG emissions due to land application of sludge are as follows	Since there are gaps in the knowledge associated with land application of sewage sludge. Few of the parameters are considered from sewage sludge compost. Moreover, we have not included the GHG emissions during sludge generation, dewatering and during the transportation of dewatered sludge to the land application site
		(i) Increased GHG emissions due to increased flux of gases at the soil–atmosphere interface
		(ii) Replacement of the synthetic fertilizers
		(iii) Carbon sequestration in the soil
		(iv) Additional water holding capacity of the soil
		(v) Improved tillage and workability of the soil
		(vi) Photosynthetic absorption of carbon by crops

Note: NA, not applicable.

Table 4. Parameters considered for evaluation of GHGs during the land application of sludge digestate.

Parameter	Quantity	Unit	Reference
Volume of wastewater	75708.0	m^3/day	Assumed
Sludge production rate	0.225	kg of dry solids/ m^3 of wastewater treated	Ghazy, Dockhorn, and Dichtl (2009); Ghazy et al. (2011)
Sludge produced during wastewater treatment	17034.3	kg dry solids/day	Calculated
Volatile solids content in sludge	65.0	%	Metcalf et al. (2004)
Total dry solids degraded during AD	40.0	%	Metcalf et al. (2004)
Digestate for land application	12051.8	Kg dry solids/day	Calculated
Case 1. low percentage of
	(w/w)
Organic carbon	18.0	(%)
Nitrogen	0.5	(%)	McFarland (2001); Sommers (1977)
Phosphrous	0.5	(%)
Case 2. high percentage of
Organic carbon	39.0	(%)
Nitrogen	17.6	(%)
Phosphrous	14.3	(%)	McFarland (2001); Sommers (1977)
Average nutrient concentration
Organic carbon
Nitrogen	28.5	(%)	McFarland (2001); Sommers (1977)
Phosphrous	9.1	(%)
	7.4	(%)
Digestate applied on the land mm
	mm
Thickness	53.4		NEBRA (2008)
Water content of sludge before land application	70.0	%	McFarland (2001)
Bulk density of sludge	1020.0	kg/m^3	McFarland (2001)

Figure 2. Net GHG emissions due to the land application of sewage sludge with different nutrients concentrations.

Table 5. Net GHG emissions due to sewage sludge land application at different nutrient concentrations.

		Case 1	Case 2	Case 3
		GHG emission (Mg CO2/yr) at
	Description	Low nutrient concentration	High nutrient concentration	Average nutrient concentration
I.	GHG reductions due to replacement of fertilizers	−40.88	−1414.97	−53.74
II.	GHG reductions due to carbon sequestration	−2.38	−515.81	−259.10
III.	GHG reductions due to additional water holding capacity	−17.71	−17.71	−17.71
IV.	GHG reductions due to improved tillage	−0.05	−0.05	−0.05
V.	GHG reductions due to photosynthetic absorption of CO2 by crops	−10.03	−10.03	−10.03
VI.	Sum of the reductions (I+II+III+IV+V)	−71.05	−1958.58	−340.63
VII.	GHG emissions due to increased flux	439.23	439.23	439.23
VIII.	GHG emissions due to energy utilization	819.91	819.91	819.91
IX.	Sum of the GHG emissions (VII+VIII)	1259.15	1259.15	1259.15
	Net GHG emissions due to land application of digestate	1188.10	−699.43	918.51
	The reduction in net GHG emissions compared to case 1	–	158.0%	22.0%

Note: Negative sign indicates a reduction in GHG emissions; positive sign indicates increased GHG emissions.

Table 6. Comparison of GHG estimation methodologies due to land application of sewage sludge.

Description			GHG reductions	GHG emissions	Net GHG emissions	Reference
Case 1 :
Organic carbon 18.0%, nitrogen 0.5% and phosphorus 0.5%			NA	686	686	IPCC
			NA	2903	2903	RTI
			−1496	1030	−465	BEAM
			−71	1259	1188	This study
Case 3:			NA	1882	1882	IPCC
Organic carbon 28.5%, nitrogen 9.1% and phosphorus 7.4%			NA	3159	3159	RTI
			−8085	4629	−3456	BEAM
			−340	1259	919	This study
Case 2:			NA	3078	3078	IPCC
Organic carbon 39.0%, nitrogen 17.6% and phosphorus 14.3%			NA	6290	6290	RTI
			−14745	8228	−6516	BEAM
			−1988	1259	−699	This study
Default values of 4.0% N and 1.5% P			−4046	2503	−1543	BEAM

GHG emissions (kg/Mg of dry solids)
CO2	CH4	N2O
25.00	−0.01	−0.19
			−223	110	−112	Lundin et al. (2004)
NA	3.18	NA	NA	392	392	Hospido et al. (2005)
17.2	−21.30	−0.19	−224	75	−148	Hong et al. (2009)
17.2	3.18	NA	NA	467	467	Niu et al. (2013)

Note: NA means not applicable; IPCC is an intergovernmental panel on climate change; RTI is research triangular institute; BEAM is biosolids emissions assessment model; negative sign indicates a reduction in GHG emissions; positive sign indicates increased GHG emissions.

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