Life cycle analysis for the production of volatile fatty acids from wastewater treatment plant sludge

Figures & data

Figure 1. General scheme of the system.

Table 1. Physico-chemical characteristics of inoculum and primary domestic wastewater sludge.

Substrate	% Total Solids (TS)	% Organic Matter^a	% Volatile solids (VS)	% Kjeldahl Total Nitrogen KTN	Chemical Oxygen Demand COD mg/L
Primary Sludge	4.88 + 0.01	69.21 + 0.01	3.67 + 0.41	0.16 + 0.01	31,600
Inoculum	5.12 + 0.49		4.21 + 0.41

^a Dry basis.

Figure 2. (a) Mass and energy flow diagram VFA production 7 d. (b) Mass and energy flow diagram VFA production 16 d.

Figure 3. Comparison of the production of 1 kg VFA 16 d and 7 d.

Table 2. Environmental impacts by impact category to produce VFAs over 16 and 7 days.

Impact category	UNIT	VFA 16 days	VFA 7 days
Terrestrial ecotoxicity	Kg 1,4-DCB	5,68E-01	3,12E-01
Non-carcinogenic human toxicity	Kg 1,4-DCB	1,94E-01	8,88E-02
Global warming	Kg CO2 eq	1,86E-01	8,86E-02
Scarcity of fossil resources	Kg oil eq	5,82E-02	2,80E-02
Marine ecotoxicity	Kg N eq	3,02E-02	1,34E-02
Ecotoxicity in freshwater	Kg 1,4-DCB	2,42E-02	1,07E-02
Human carcinogenic toxicity	Kg 1,4-DCB	8,53E-03	3,99E-03
Land use	m^2a crop eq	1,78E-03	1,06E-03
Ionizing radiation	KBq Co-60 eq	9,67E-04	6,33E-04
Terrestrial acidification	Kg SO2 eq	7,69E-04	3,63E-04
Water consumption	m^3	7,23E-04	5,12E-04
Ozone formation, Terrestrial Ecosystems	Kg NOx eq	4,47E-04	2,35E-04
Ozone formation, Human health	Kg NOx eq	4,43E-04	2,32E-04
Scarcity of mineral resources	Kg Cu eq	3,87E-04	1,91E-04
Fine particle formation	Kg PM2.5 eq	2,76E-04	1,33E-04
Freshwater eutrophication	Kg P eq	8,67E-05	4,26E-05
Marine eutrophication	Kg N eq	6,16E-06	3,44E-06
Stratospheric ozone depletion	Kg CFC11 eq	1,01E-07	4,73E-08

1,4-DCB: Kilograms of 1,4-dichlorobenzene equivalents; kBq Co-60 eq: Cobalt-60 equivalent radioactivity.

Figure 4. (a) Fossil resources to produce 1 kg of VFAs in 16 d. (b) Fossil resources to produce 1 kg of VFAs in 7 d.

Figure 5. (a) Contribution per process to fossil resource VFAs 16 d. (b) Contribution per process to fossil resource VFAs 7 d.

Figure 6. (a) Global warming to produce 1 kg of VFAs in 16 d. (b) Global warming to produce 1 kg of VFAs in 7 d.

Figure 7. (a) Contribution per process to global warming VFAs 16 d. (b) Contribution per process to global warming VFAs 7 d.

Table 3. Comparison of LCA results of VFAs with other studies.

	Study		Tong et al. (2018)			Jin et al. (2015)	Di Maria and Micale (2014)	Katakojwala and Mohan (2020)			Elginoz et al. (2020)	Xu et al. (2015)		Gálvez et al. (2021)
Impact category	VFA16 d	VFA 7 d	AD com	AD Inci	ADgas	AD inc	AD com	MCC1	MCC2	MCC3	VFA	AD of food waste and sludge	AD of food waste	VFA of food waste	VFA microalgae food	VFA, food waste +  composting	VFA, microalgae waste +  composting
Terrestrial ecotoxicity	5,68E-01	3,12E-01		4,48E-02	5,61E-03			2,30E-01	1,97E-01	1,35E-01	1,18E-04	9,33E-07	1,18E-06	4,93E-02	1,74E-02	2,80E-01
Non-carcinogenic human toxicity	1,94E-01	8,88E-02						4,03E + 01	3,22E + 01	2,29E + 01	5,70E-03	8,12E-03	7,30E-03	9,93E + 00	4,12E + 00	2,97E + 01
Global warming	1,86E-01	8,86E-02	9,41E + 01	9,25E + 01	3,85E + 01	9,70E-02	1,81E-01	2,64E + 03	2,04E + 02	1,47E + 02	1,46E-02	2,13E-01	1,69E-01	3,52E-01	1,52E-01	4,56E-01	1,30E-01
Marine ecotoxicity	3,02E-02	1,34E-02						2,38E + 05	1,86E + 05	1,34E + 05		1,70E-04	1,40E-04	1,19E + 01	4,91E + 00	3,56E + 01
Ecotoxicity in freshwater	2,42E-02	1,07E-02				4,89E-03		9,51E-01	7,50E-01	5,43E-01	4,37E-03	1,70E-04	1,40E-04	5,41E-04	1,39E-04	2,54E-03
Ionizing radiation	9,67E-04	6,33E-04										6,40E-04	1,04E-03	4,55E-03	1,86E-03	8,77E-03	8,76E-04
Terrestrial acidification	7,69E-04	3,63E-04					1,70E-04	9,44E-01	7,44E-01	5,31E-01	7,47E-05	6,90E-04	4,80E-04	2,05E-04	9,13E-05	1,22E-05	1,46E-04
Water consumption	7,23E-04	5,12E-04										1,96E-05	7,44E-05	1,21E-03	8,03E-04	2,07E-03	5,91E-04
Ozone formation, Terrestrial Ecosystems	4,47E-04	2,35E-04	1,20E-02	1,68E-02	1,40E-02		1,02E-04							4,19E-04	1,81E-04	5,10E-04	1,63E-04
Scarcity of mineral resources	3,87E-04	1,91E-04										2,40E-04	1,81E-03	2,04E-04	8,43E-05	1,09E-03
Fine particle formation	2,76E-04	1,33E-04										2,60E-04	1,90E-04	8,60E-05	3,49E-05	1,44E-04	2,21E-05
Freshwater eutrophication	8,67E-05	4,26E-05	4,00E-02	7,31E-02	6,86E-02	2,00E-05	6,30E-04	1,17E-01	9,06E-02	6,48E-02	1,75E-05	6,25E-06	4,64E-06
Marine eutrophication	6,16E-06	3,44E-06										1,40E-04	1,00E-04
Stratospheric ozone depletion	1,01E-07	4,73E-08		1,98E-06	1,12E-05			4,10E-06	5,13E-06	2,81E-06		2,22E-10	3,98E-10		1,16E-06		2,19E-06

Incineration (Inci), Anaerobic digestion (AD) followed by composting (ADcom), AD followed by incineration (ADinci), and AD followed by gasification (ADgas).

Red blocks have higher values, and green blocks have lower values per impact category.

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Data availability statement

The authors confirm the statement of data availability.