Page 207 - Materials Chemistry, Second Edition

188 Life Cycle Assessment of Wastewater Treatment

TABLE 9.3
Main Values of Sludge Characterization Parameters

Primary Secondary Anaerobically
Parameter Sludge Sludge Digested Sludge Compost
pH 6.48–7.15 6.66–7.20 8.40–8.61 6.55–8.29
Moisture content (%) 95.7–96.8 96.2–96.8 75.3–80.2 28.6–36.3
Dryness (%) 3.23–4.28 3.17–3.81 19.8–24.7 63.7–71.4
Organic matter (%) 62.6–74.4 73.3–78.7 48.6–52.1 20.2–26.6
Total nitrogen (%) 2.01–2.48 4.22–6.28 3.27–4.04 2.54–4.52
Total phosphorus (%) 0.13–0.28 0.28–0.39 0.26–0.38 0.06–0.10

pK values) (Table 9.2) but also by the different composition of primary and sec-
a
ondary sludge (Table 9.3) resulting in different retention mechanisms. The higher
concentrations of some compounds in primary sludge could be due to retention by
electrostatic interactions, whereas the higher concentrations of other compounds in
secondary sludge may be due to the hydrolysis of conjugates, releasing the pattern
compound, and to sorption enhancement of non-ionic compounds, due to the higher
organic matter content of secondary sludge (Table 9.3), by non-ionic van der Waals
interactions (Martín et al., 2012a; Ternes et al. 2004; Verlicchi and Zambello, 2015).
After anaerobic digestion, the concentration levels of most of the pharmaceuticals
decreased by biodegradation (Figures 9.1 and 9.2). Nevertheless, the concentration of
some compounds, such as caffeine and 17β-estradiol (Figure 9.2), increased.

9.3.2 occurrence anD faTe of pHarMaceuTicals in seWage
sluDge froM DifferenT TreaTMenT TecHnologies
Sludge stabilization can be carried out by anaerobic digestion (in anaerobic treat-
ment plants [AnTP] and in anaerobic wastewater stabilization ponds [AnWSPs]) or
by aerobic digestion (in aerobic treatment plants [AeTP] and in composting plants
[CP]). AnWSPs are low-cost urban wastewater treatments based on shallow ponds
typically used to treat wastewater from small towns. Aerobic digestion is a bacterial
process in the presence of oxygen. Composting is a natural process of microbial
decomposition of organic matter enhanced by sludge aeration by regularly turning.
In previous work by our group, the 16 above-mentioned pharmaceuticals (Table 9.2)
together with the anti-inflammatory acetaminophen; the antibiotics ciprofloxacin,
norfloxacin, and ofloxacin; the β-blocker atenolol; and the lipid regulator bezafibrate
were analyzed in sewage sludge from four AnTPs, three AeTPs, three AnWSPs, and
a CP (Martín et al., 2015). Four sampling campaigns in a 1-year period were car-
ried out. The most contaminated samples were primary sludge from AnTPs (mean
concentration: 179 ng g d.m.), mixed sludge (mixture of primary and secondary
−1
−1
sludge) from AeTPs (mean concentration: 310 ng g d.m.), and lagoon sludge from
−1
AnWSPs (mean concentration: 142 ng g d.m.). A higher decrease was observed
after anaerobic digestion than after aerobic digestion, which can be explained by