# Evaluation of the impact of urbanism on source separation system by life cycle assessment

Mathilde Besson, L. Tiruta-Barna, Etienne Paul, M. Sperandio

<figure><img src="image_1.png" /></figure>

To cite this version:

Mathilde Besson, L. Tiruta-Barna, Etienne Paul, M. Sperandio. Evaluation of the impact of urbanism on source separation system by life cycle assessment. IWA Wastewater, Water and Resource Recovery Conference, IWA, 2022, Poznan, Poland. hal-04931863

HAL Id: hal-04931863

https://hal.science/hal-04931863v1

Submitted on 6 Feb 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Evaluation of the impact of urbanism on source separation system by life cycle assessment

M Besson*¹, L Tiruta-Barna*², E Paul*³, M Spérandio*⁴

* TBI, Université de Toulouse, CNRS, INRAE, INSA, Toulouse, France - 135 avenue de Rangueil,
¹mbesson@insa-toulouse.fr ²lbarna@insa-toulouse.fr ³paul@insa-toulouse.fr ⁴sperandi@insa-toulouse.fr

**Abstract:** This study aims to assess the effect of different urban configurations regarding the choice of different source separation scenarios (urine, blackwater, greywater treatment). Six different urban configurations representing the different districts in European cities have been tested. The results demonstrate the enormous influence of urbanism typology on the results of life cycle assessment for source separation systems.

**Keywords:** Source separation, Urbanism, Life Cycle assessment

## Introduction

Source separation of domestic wastewater can be a relevant strategy to recover resources from wastewater and especially nutrients (Besson et al., 2021). It is a complementary strategy with water resource recovery facility (WRRF) for replacing conventional wastewater treatment. Source separation can be beneficial for limiting the impact of wastewater treatment on climate change. The nitrogen from excreta separation will no longer enter the treatment plants and N₂O emissions from biological treatment of nitrogen is reduced, with in the meantime an increase of the avoided impact linked to the production of conventional fertilisers (Besson et al., 2021; Bisinella de Faria et al., 2015). However source separation of urine or blackwater present different environmental assessments varying among the studies (Remy, 2010; Thibodeau et al., 2014). From literature it comes that the type of urbanism and the scale of implementation can affect the environmental assessment. Differences in urban typologies (individual housing or collective buildings) might have effects on the type of sanitation to establish. To our knowledge, linking urban configuration and source separation systems through environmental assessments has not yet been performed. This study aims to fulfil these gaps by combining the modelling of wastewater treatment with different urban configurations. Limits of each system are then addressed with an urban planning approach in order to highlight the feasibility of the most promising system(s).

## Material and Methods

The six urban configurations identified by (Bonhomme, 2013) were considered: discontinuous pavilions (DP), continuous pavilions (CP), discontinuous buildings (DB), continuous buildings (CB), city centre (CC), high-rise tower (HT). An automatic district generator was developed considering a number of specific constraints: (1) road constraints, width and density, (2) number of buildings in accordance with the land coverage ratio and the surface of each building, (3) positioning the buildings randomly in the district, (4) number of people thanks to inhabitant density and the number of tertiary buildings. The approach described in (Besson et al., 2021) was used to model the production, the collection and transport of wastewater and integrate the results in a life cycle assessment. Four wastewater management systems were studied (Figure 1): A) reference scenario based on
centralised management at WRRF, B) urine separation and transport to WWTP for dedicated valorisation as struvite and ammonium salt, C) separation of blackwater and greywater with decentralised treatment of blackwater, and finally D) separation of blackwater and greywater with fully decentralised treatment system.

## Results and Discussion

While all the LCA impacts categories were analysed, the climate change impact at midpoint level was represented for each urbanism typology and for different sanitation systems (Figure 2). Urine source separation always presents an improvement compared to the reference scenario, showing reduction from 20% for the discontinuous pavilions up to 60% for the high-rise towers. The benefit of urine separation scenario is due to reduction of N₂O emissions, and nutrient reuse in agriculture. The lower benefit for low density urbanism is due to the higher contribution of the sewer infrastructure in the district for wastewater collection.

For Black Water scenario, the impact on climate change is almost similar as reference wastewater management for low density urbanism. The benefit of BW management scenario increases for higher urban density and reaches 40% reduction of greenhouse gas for high-rise district. The major improvements of this scenario come from better nutrient recovery and lower N₂O emissions. The contribution analysis shows that the limits of BW scenario comes from energy demand of vacuum sewer, ... heat or electricity demand. For both BW and BW-GW scenarios, heat impact depends poorly on the urban typology. On the other hand, electricity balance depends on urban configurations as more electricity is produced with larger scale cogeneration units in high density area, reducing the external needs. The PE density influences the contribution of sewer infrastructure (for both vacuum and gravity sewer) on climate change impact.

When greywater reuse is also included in the alternative scenario (BW-GW) the system becomes fully decentralised. This scenario presents in all urbanism a higher climate change impact compared to the reference (WRRF) except for the high-rise tower urbanism. This is due mainly to the higher electricity needs for treatment of wastewater with a technology dedicated for reuse (membrane bioreactor). However, it can be noted than high-rise towers in BW-GW systems can reach the same impact than the reference scenario. This means that it could be possible to reuse greywater in specific conditions as a climate change mitigation strategy and avoid to increase the climate change impact. Moreover this balance is sensitive to the climate change impact of the drinking water production system which is replaced.

## Conclusions

Globally this study demonstrates the enormous influence of urbanism typology on the results of life cycle assessment of source separation systems. This should be considered for future studies and recommendations.

The urine system provides a significant improvement on climate change impact in all the urban configurations. For the blackwater management system, low densely populated areas were not significantly different from the reference but benefit is significant for dense area. Finally, the decentralised greywater treatment degraded the climate change impact for all the urban configurations, except for the high-rise tower where the impact was similar to the reference scenario.
## References

Besson, M., Berger, S., Tiruta-barna, L., Paul, E., Spérandio, M., 2021. *Environmental assessment of urine, black and grey water separation for resource recovery in a new district compared to centralized wastewater resources recovery plant*. *Journal of Cleaner Production* 301, 126868.

Bisinella de Faria, A.B., Spérandio, M., Ahmadi, A., Tiruta-Barna, L., 2015. *Evaluation of new alternatives in wastewater treatment plants based on dynamic modelling and life cycle assessment (DM-LCA)*. *Water Research* 84, 99–111.

Bonhomme, M., 2013. *Contribution à la génération de bases de données multi-scalaires et évolutives pour une approche pluridisciplinaire de l'énergétique urbaine* (Thèse de doctorat en Génie Civil). Laboratoire de recherche en architecture et Laboratoire matériaux et durabilité des constructions - Université de Toulouse, France.

Remy, C., 2010. *Life cycle assessment of conventional and source separation systems for urban wastewater management*.

Thibodeau, C., Monette, F., Bulle, C., Glaus, M., 2014. *Comparison of black water source-separation and conventional sanitation systems using life cycle assessment*. *Journal of Cleaner Production* 67, 45–57.

## Figures and Tables

<figure><img src="image_3.png" /><figcaption>**Figure 1** Presentation of the four scenarios. WRRF: Wastewater recovery facility, AD: Anaerobic digester, PPTSTRU: Struvite precipitation, TMCS: transmembrane chemisorption, UASB: upflow active sludge blanket, MBR: membrane bioreactor, ANAER: anaerobic tank, ANOX: anoxic tank, AER: aerated tank, PANOX: post-anoxic tank, PAER: post aerobic tank, THK: thickening, PTHK: post-thickening, DW: dewatering.</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 2** Difference in climate change impact for each scenario compare to reference one regarding scale and typology. DP: discontinuous pavilions, CP: continuous pavilions, DB: discontinuous buildings, CB: continuous buildings, CC: city centre, HT: high-rise tower</figcaption></figure>