Biodegradable substrate

Others would extend the fertiliser concept to the simultaneous addition of readily biodegradable substrates along with the fertiliser nutrients to stimulate the growth of contaminant-degrading organisms most rapidly, and to aid in the rapid utilisation of the fertiliser nutrients before they might be leached from the contaminated area. The specific requirements for the most efficacious substrates is an area of current research. 

Preservation of readily biodegradable substrates in sewers may be crucial in case of denitrification and phosphorus removal in advanced treatment processes. 

Ss. soluble substrate (readily biodegradable substrate) directly available for the microorganisms after diffusion into the cell... 

SF = readily (fermentable) biodegradable substrate SA = volatile acids/fermentation products Ss = readily biodegradable substrate (Ss = SF+ SA)... 

Xs = slowly biodegradable substrate XAUT = autotrophic, nitrifying biomass XpHA = stored polyhydroxyalkanoate XPA0 = phosphorus-accumulating organisms... 

KSw = saturation constant for readily biodegradable substrate (gCOD m-3)... 

Suspended biomass growth results in the removal of readily biodegradable substrate. A yield constant, YHw, typically about 0.55 g COD biomass produced... 

Laboratory and mixed field/laboratory studies have confirmed that half-order kinetics for DO surface removal rates may be a reasonable approximation for sewer biofilm (Raunkjaeretal., 1997 Bjerre etal., 1998b). These results also showed the influence of readily biodegradable substrate. Furthermore, temperature dependency limited by diffusion is included (Nielsen et al., 1998). The following equation for the aerobic growth rate was therefore used ... 

Hydrolysis of particulate substrates produces readily biodegradable substrate for the biomass (cf. Figure 5.4 and Section 3.2.3). The kinetics of the hydrolysis, following the concept of the activated sludge model one, is described in Section 2.2.2. The following interpretation of hydrolysis of wastewater in a sewer is considered particulate substrate is available in the bulk water phase, and biomass in the bulk water and biofilm—assuming a reduced activity in the biofilm—is taken into account. Under these conditions, the rate of hydrolysis, rhydr, for each of the hydrolyzable fractions, n, is as follows ... 

C. Unpublished results of nitrate removal rates for biofilms under sewer conditions have shown values around 0.05 gN03-N m-2 h-1 for normal wastewater from households and from 0.10-0.18 for wastewater with readily biodegradable substrate. 

The biomass yield constant was, according to Poulsen (1997), about 0.38 gCOD gCOD-1. Aesoey et al. (1997) showed that 4.8 gCOD gN03-N-1 is removed when readily biodegradable substrate is available. If hydrolysis limits the transformations, this value was reduced to about 50%. 

Anaerobic hydrolysis this process transforms the hydrolyzable substrate, Xsn, into fermentable, readily biodegradable substrate,. S /,. 

As shown in Figure 6.8, the most important part of the anaerobic sulfur cycle in terms of the sulfate respiration process can be integrated with the anaerobic carbon cycle. A fractionation of the readily biodegradable substrate (Ss) into SF and SA fits well to the anticipation that mainly SF is used by the sulfate-reducing biomass in sewer biofilms. By integrating the sulfide formation in this way, a simple conceptual approach is obtained instead of the traditional empirical descriptions as depicted in Table 6.1. 

The results in Figure 6.9 show that the production rate of readily biodegradable substrate (Ss) by the anaerobic hydrolysis is larger than the removal rate. It is a major result that readily biodegradable substrate is not just preserved but produced. This fact has positive implications on the subsequent treatment processes in terms of denitrification and biological phosphorus removal. On the other hand, it is negative if wastewater treatment is only required in terms of BOD removal. 

Ksw Saturation constant for readily biodegradable substrate 1.0 gCOD nr3... 

Determination of central model parameters (cf. Section 7.2.1). OUR versus time measurements of incoming wastewater to a sewer system modified by the addition of readily biodegradable substrate, e.g., acetate. 

An OUR experiment is performed on a wastewater sample from the influent to the sewer system in question. The sample is modified by addition of readily biodegradable substrate, typically acetate or glucose. The following four process parameters are explicitly determined based on this experiment ... 

The experiment, or preferably a number of parallel experiments, is carried out until the originally available readily biodegradable substrate and the fast hydrolyzable substrate are depleted. For typical domestic wastewater, this is... 

Before adding the readily biodegradable substrate, the maintenance energy requirement of the active biomass should ideally correspond to the amount of readily biodegradable substrate produced by hydrolysis of the slowly biodegradable COD fraction, i.e., an equilibrium corresponding to an almost constant OUR must be seen. 

The active biomass that is available must react directly on (i.e., show an immediate exponential growth response on) the readily biodegradable substrate that is added. 

As shown in Figure 7.4, an OUR experiment of a wastewater sample reflects the different phases of activity that the heterotrophic biomass is exposed to depending on the availability of the substrate. If an OUR experiment is carried out under both substrate-nonlimited and substrate-limited conditions, the different COD components can be determined. Such conditions exist during an OUR experiment where readily biodegradable substrate is available at the beginning of the experiment. 

The determination of the COD components depends on the fact that the substrate uptake can be experimentally related to the OUR curve. The heterotrophic yield constant, YHw, that is experimentally determined from procedure number 1, Section 7.2.1, relates the oxygen uptake to the readily biodegradable substrate that is consumed irrespective of its origin, being either directly available or continuously produced from hydrolyzable COD fractions. 

Basically, the procedure for determination of XBw(t0) requires availability of readily biodegradable substrate at t = 0, ideally not less than 10-15 gCOD nr3,... 

The VFAs, primarily formate, acetate, propionate, n-butyrate and isobutyrate, can be determined analytically on an ion chromatograph (Standard Methods for the Examination of Water and Wastewater, 1998). Determination of fermentable, readily biodegradable substrate, SF, and fermentation products, SA, in units of COD requires that the VFA components be converted to this unit. The following example using formate demonstrates this ... 

The relationship between readily biodegradable substrate, Ss, fermentable, readily biodegradable substrate, Sp, and fermentation products, SA, is defined as ... 

DETERMINATION OF THE FORMATION RATE FOR READILY BIODEGRADABLE SUBSTRATE ... 

FIGURE 7.14. Net generation rates of readily biodegradable substrate, Ss, under anaerobic conditions in wastewater. The results originate from 19 experiments carried out on wastewater at the inflow to two treatment plants. 

C02 exists under anaerobic conditions in wastewater. They also found that typically 50% of the C02 was produced by the sulfate-reducing bacteria, the other half by the fermenting biomass. However, the net production rate of Ss was typically about 70% of the total produced Ss by anaerobic hydrolysis [Equation (7.10)]. Hence, this equation may, even in a reduced form, be valuable for the estimation of the production of readily biodegradable substrate under anaerobic conditions. 

The result of the aerobic scenario in terms of quality changes of the wastewater in the intercepting sewer is shown in Table 8.2. The in-sewer treatment is assessed by the changes that take place in the easily biodegradable substrates (readily biodegradable and fast hydrolyzable substrates) and in the... 

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