Water SA 48(1) 1–20 / Jan 2022 Research paper

Overview

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• Part 3: Measuring the organics composition
• Water Research Group, Dept of Civil Engineering, University of Cape Town, Rondebosch 7700, Cape Town, South Africa
• BMP from a stand-alone test to a bio-reactor on which a range of additional tests are made to determine the Received: 22 February 2016
• composition of biodegradable organics. The AugBSP, which is based on biological sulphate reduction, can Accepted: 28 December 2021
• The material content flux of the reactants in the influent for a continuous system, or the initial (CC BY 4.0)
• physical and biodegradable characteristics (Fig. 1).
• non-settleable constituents) and primary sludge (all 5 non-settleable in the water flow plus the two
• (WRRF) comprising both aerobic and anaerobic unit operations (Ekama, 2009; Ikumi et al., 2015).
• (2014) showed that the influent and endogenously generated unbiodegradable particulate organics,
• ISSN (online) 1816-7950 1
• Figure 1. Raw wastewater and settled characterization divides raw wastewater organics into seven organics groups: three physical (dissolved,
• reaction product water (Van Zyl et al., 2008). If the influent
• curves over the 4–10 pH range to see if there are additional weak
• volatile fatty acids (VFA), OP, FSA and free (H2S) and saline (HS-)
• al., 2002). The proportion and composition of fats, carbohydrates
• sulphide (FSS) (Westergreen et al., 2012).
• demand (COD), carbon (C), nitrogen (N), phosphorus (P) and chromatography or 5-point titration: Moosbrugger et al., 1993;
• sulphur (S) match the CxHyOzNaPbSc composition of the group. Vannecke et al., 2015; see also Part 4 of this series – Ekama et
• We adopt the general approach of assigning a single composition al., 2022) and can be represented by acetate, the elemental
• Standard Methods (1998). compositions of the organics groups is not necessary – the mass
• ELECTRON DONOR ORGANICS COMPOSITION most CO2 produced from C content of the organics is stripped
• c ≡ C f C /12 H f H /1O f O /16 N f N /14 Pf P /31S f S /32 (1) is constant because varying organics composition affects the gas
• ch/ x 2021b). So, measurement of the organics elemental composition
• c ≡ C1H y / x O z / x N a/ x Pb/ x S c / x (2)
• if particulate) and the right-hand-side of Eq. 1 gives the three phase (aqueous–solid–gas) plant-wide bioprocess models
• stoichiometric composition of 1 g of the e− donor organics. The are written in a general way, which requires the composition
• ratios, viz.: biomass, as inputs to the models (Brouckaert et al., 2010; Ikumi et
• al., 2011; Brouckaert et al., 2021b).
• αN,i and αP,i of Grau et al. (2007) and Volcke et al. (2006), were the i waste is zero, there are six unknowns in Eqs 1 to 3, either x, y, z, a,
• ELEMENTAL COMPOSITIONS represent the products of the COD test (i.e. CO32−, H2O, NH4+,
• PO43−, SO42−, which all have an EDC relative to COD of zero as in
• Eqs 10 and 11 in Brouckaert et al., 2021b (Part 2), yields:
• biomass. Actually, it is the composition of these two components f O  16
• known composition in the aqueous and gas phases involved in f H  19 (1  f cv  12
• phase concentrations caused by these two components can be Details of the derivation of Eqs 4 and 5 are given in the Appendix.
• used to determine their composition. Sometimes, for autotrophic Equations 4 and 5 have been set up to maintain the mass balance
• can be assumed (like C1H1.4O0.4N0.2, or the better known C5H7O2N, six mass ratios known (some zero), the molar composition of
• Porges and Hoover, 1952) because the net biomass yield (E) is the organics (or biomass) can be determined from Eq. 1. Then
• very low, usually <10% of the electron (e−) donating capacity with Eq. 2, this molar composition for 1 g organics can by scaled
• is high (>40%), reasonably accurate estimates of the biomass mass ratios fcv = 1.416 gCOD/gVSS, fC = 0.531 gC/gVSS and fN =
• composition are required to accurately calculate (with steady state 0.124 gN/gVSS (with fP and fS = 0) yield fO = 0.283 gO/gVSS and fH
• or dynamic models) the bioprocess reactants (nitrate and oxygen = 0.0619 gH/gVSS from Eqs 4 and 5. Then from Eq. 1 the molar

Methods (brief)

• as C xHy OzNaPbS c, are identified. Examples of the calculation procedure from the test results are given. anaerobic digestion
• anaerobic digestion dynamic modelling, are as accurate as the analytical measurements for determining the biosulphide potential
• with that of Anaerobic Digestion Model No 1 (ADM1, Batstone et
• errors in the large contributors to the mass of the organics (fC, each of 29 sewage sludge samples from various WRRF and tested
• balance between all the measured mass ratios to establish the random sludge sample within 1.15%.
• ments on samples withdrawn at regular intervals from the Test generated by both the biomass endogenous respiration and the
• Unfiltered samples; 2Filtered samples; 3H2CO3 alk in mg/L as CaCO3 for the BMP test; 4mL gas at 20°C. COD of CH4 gas = mL x 273.15/(273.15 + 20)/22.4 x
• the VSS difference. Also, samples taken during the test reduce
• The AugBSP test procedure is proposed to obviate the gas volume alk (Poinapen et al., 2009). The filtered sample is analysed for FSA,
• measurement error and correction problems. Loewenthal et al. (2005) FSS and OP. After centrifugation of the sample collected without
• plunger and clampable sample withdrawal hose (Fig. 2). pH has to al., 2021b), in the Control, the C in the biomass endogenously
• because pH will rise quickly in extracted samples due to loss of − Cstart) difference in H2CO3 alk (from which the difference in
• full with no head space, when a sample is required the sample calculated (Table 5). Similarly, the N and P content of the biomass
• screwed down to force out a sample from the reactor. Two samples and OP concentrations. Also, the COD of the biomass ‘lost’
• are collected and treated in the manner outlined by Poinapen et al. (fcv) is given by the (Cend − Cstart) difference in FSS (converted to
• (2009), viz., one collected in a sample jar with 1 drop 10N NaOH COD, i.e. mgFSS-S/L x 64/32) or SO42− (converted to COD, i.e.
• and the other in a sample jar without NaOH. The sample with mgSO4-S/L x 64/32) concentrations. Finally, the VSS of the
• (and CO2) and the organics and FSS determined via the COD or All these measurements are on aqueous samples which can

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