Treatment of Source-Separated Blackwater: A Decentralized Strategy for Nutrient Recovery towards a Circular Economy

Abstract

Using a filter medium for organic matter removal and nutrient recovery from blackwater treatment is a novel concept and has not been investigated sufficiently to date. This paper demonstrates a combined blackwater treatment and nutrient-recovery strategy and establishes mechanisms for a more dependable source of plant nutrients aiming at a circular economy. Source-separated blackwater from a student dormitory was used as feedstock for a sludge blanket anaerobic-baffled reactor. The effluent from the reactor, with 710 mg L −1 NH 4-N and 63 mg L −1 PO 4-P, was treated in a sequence of upflow and downflow filtration columns using granular activated carbon, Cocos char and polonite as filter media at a flow rate of 600 L m −2 day −1 and organic loading rate of 430 g chemical oxygen demand (COD) m −2 day −1. Filtration treatment of the anaerobic effluent with carbon adsorbents removed 80% of the residual organic matter, more than 90% of suspended solids, and turbidity while releasing more than 76% NH 4-N and 85% of PO 4-P in the liquid phase. The treatment train also removed total coliform bacteria and E. coli in the effluent, achieving concentrations below detection limit after the integration of ultraviolet (UV) light. These integrated technological pathways ensure simultaneous nutrient recovery as a nutrient solution, pathogen inactivation, and reduction of active organic substances. The treated nutrient-rich water can be applied as a source of value creation for various end-use options.

Rheological characterisation of synthetic and fresh faeces to inform on solids management strategies for non-sewered sanitation systems

“…Such units could recover faecal solids to a dry friable form which in turn reduces volume, thereby improving the economics of transport as well as reducing pathogenic risk ( Brockmann, 1973 ; Naidoo et al, 2020 ). Furthermore, this concentrated faecal sludge fraction comprises solely of blackwater constituents rich in nutrients and organics with direct opportunity for nutrient or energy recovery, encouraging local economic opportunities for sustainable sanitation ( Eshetu Moges et al, 2018 ; Forbis-Stokes et al, 2016 ; Harder et al, 2019 ; Onabanjo et al, 2016 ). As such, localised solid/liquid separation could enable a community accepted shift towards sustainable faecal sludge management ( Mikhael et al, 2014 ).…”

Nutrient Recovery from Anaerobically Treated Blackwater and Improving Its Effluent Quality through Microalgae Biomass Production

“…Anaerobically digested, post-treated (after filtration and ultraviolet (UV) treatment), and hygienized blackwater effluent [29] was used as a substrate for a continuous microalgae culture.…”

“…However, increased nitrite and nitrate concentrations have been registered later due to the installation of a membrane bioreactor after the sludge blanket anaerobic baffled reactor to remove dissolved methane but the ammonium nitrogen still represented more than 80 % of the inorganic N. Similarly, about 85% of the P in the effluent of the anaerobic reactor was orthophosphate. Although, NH 4 -N and PO 4 -P have been the main forms of N and P, the N in treated blackwater is taken as the sum of NH 4 -N, NO 3 -N and NO 2 -N. After diluting the treated blackwater, the concentrations of Mg and other micronutrients were low in the treated blackwater treatment [29], so that these nutrients were supplemented to avoid limiting the growth of C. sorokiniana. The NH 4 :PO 4 ratio in the treated blackwater ranges from 11 to 14 which is close to the required Redfield ratio of 16:1 N:P ratio usually reported for phytoplankton [31].…”

“…After the chemostat stabilized with the defined medium at a dilution rate of 1.38 d −1 , the medium was replaced by 10% and 20% treated blackwater, respectively, as a hygienized nutrient solution from anaerobically digested blackwater effluent [30] and operated with the same dilution rate of 1.38 d −1 . For optimizing the nutrient uptake MgSO 4 •7H 2 O (0.1 g L −1 ), KH 2 PO 4 /K 2 HPO 4 , NaHCO 3 (0.084 g L −1 ), CaCl 2 •2H 2 O (0.05 g L −1 ) and 1 mL L −1 Hutner's trace elements [29] were added in some of the experiments (see results).…”

Evaluating Circular Economy under a Multi-Parametric Approach: A Technological Review

“…At the context of human wastewater stream nutrients, which are highly diluted by storm water and groundwater intrusion as well as other sources, the need for an innovative solution to reduce the environmental impact simultaneously with the increased demands in water, energy and food, is a necessity [59,60]. According this, domestic wastewater can potentially contribute to the nexus of water, energy and plant nutrient supply, with regard to the CE design [61,62]. Many blackwater technologies treatment of novel concepts are stressed out, being in an infant stage to date [61].…”