Li Zifu

Experimental study on rheological characteristics of high solid content sludge and it is mesophilic anaerobic digestion

Compared to conventional low solid content anaerobic digestion, high solid content anaerobic digestion can offer attractive advantages such as higher biogas generation and smaller reactor volume demand. However, high solid content sludge has the negative impacts on the anaerobic digestion for mixing and mass transfer efficiency, which should be investigated in order to improve mixing and mass transfer effects. In the first part of this study, the rheological characters of high solid content sludge was studied using the DNJ-1 rotating viscometer. The second part of the experiment was conducted by using an anaerobic reactor (10 l) to evaluate the potential biogas production and mesophilic anaerobic process stability. This was operated at mesophilic condition (37±1)°C with high solid content (11% total solid). The results showed that the sludge belongs to the pseudoplastic non-Newtonian fluid which has the characteristics of the shear thinning. Under the optimal mixing and mesophilic conditions, the experime...

Performance of alkaline pretreatment on pathogens inactivation and sludge solubilization

Inactivation of pathogen indicators (i.e., faecal coliforms, Salmonella spp., faecal streptococcus, and helminth eggs) were investigated during alkaline pretreatment (pH=10 and 12) in this study. The performance of alkaline pretreatment on the inactivation pathogens, kinetic of pathogens inactivation and sludge solubilization was evaluated. Results of alkaline pretreatment showed that the complete inactivation periods of pathogens time were 1.5 d, 1.5 d, 2 d, 2.5 d, 3 d, 3 d and 3 d for faecal sludge total solids (TS) of 1%, 2%, 4%, 6%, 8%, 10% and 12%, respectively. The kinetics of pathogen inactivation can be predicted better by Weibull than the first-order model. Meanwhile, the relationship between alkaline pretreatment time and the TS content of the sludge agrees with the exponential equation (y =1.3543e, 1% ≤ x ≤ 8%) and logarithmic equation (y =3, 8% ≤ x ≤ 12%). Furthermore, alkaline pretreatment can improve sludge solubilization and has a more significant effect on protein solubilization than on soluble chemical oxygen demand (SCOD).

Assessment of metals in dry-toilet collected matters from suburban areas of Ulaanbaatar, Mongolia, using biosolids quality guidelines and potential ecological risk index

Dry-toilet collected matter (DCM) from traditional dry-toilet pits are a potential health and ecological risk in suburban areas. In this study, the characteristics of metals in DCMs from suburban areas of Ulaanbaatar were surveyed. The results indicate that DCMs contain a high percentage of organic matter and nutrients, while heavy metals are at low levels, which shows good agricultural potential. The concentration ranges of Cr, Cu, Hg, Ni, Pb, and Zn were 11±5, 46±9, 0.08±0.05, 9±3, 17±9, and 338±86 mg·kg−1, respectively. The concentration of Cd was below 0.5 mg·kg−1, and a high positive relation was shown between chromium and nickel concentrations. The heavy metals in DCMs were safe for land application but Zn in DCMs was close to the effects range median (ERM), which is toxic in some cases, such as amphipod bioassays. Because it is mandatory to treat DCMs to reduce pathogens, in the case of heavy metal enrichment and agricultural reuse, composting or pyrolysis are better choices than incineration. Compared with global soil background values, the heavy metals in DCMs showed a low level of ecological risk, but a medium level when compared with Mongolian soil background values. The ecological risk of six heavy metals was in the descending order Hg>Cu>Zn>Pb> Ni>Cr and the contribution rate of Hg exceeded 60%.