Characterization of raw sludge, chemically modified sludge and anaerobically digested sludge in Hong Kong

Abstract

Chemically Enhanced Primary Treatment (CEPT) or Chemically Assisted Primary Sedimentation (CAPS) is being employed at the new sewage work on Stonecutters Island as part of the Strategic Sewage Disposal Scheme (SSDS) in Hong Kong. CAPS involves the use of chemical coagulants (such as lime or ferric chloride) to induce coagulation or flocculation and let these finely-divided particles form large aggregates (floc) so that they can settle out within a reasonable period of time. In this study, five sludge samples collected from different sewage treatment plants in Hong Kong were physically and chemically characterized. They were chemically modified sludge from Stonecutters Island (CAPS) raw sludge from Tai Po and Yuen Long Sewage Treatment Plant (STP) (rTP & rYL) and anaerobically digested sludge from Tai Po and Yuen Long STP (dTP & dYL). It was found that CAPS sludge was better than other 4 sludge samples in terms of settleability and dewaterability. CAPS sludge contained significant higher amounts (p<0.01) of extractable compounds than other sludges (except NO3− for dTP, NH4+ and PO43− for dYL). The concentration of total N and P in CAPS sludge were significantly higher (p<0.01) than other sludges (except dYL). The concentrations of total Cu, Pb, Ni, Cd, Cr and K in the CAPS sludge were also significantly higher (p<0.01) than other sludge samples. Most of the metals (Cr, Pb, Cr and Zn) in CAPS sludge were associated with the organically-bounded phase. It is concluded that there are significant differences in both physical and chemical properties between the chemically modified sludge and biological treated sludges.

Ultrasound propagation studied using the discrete kinetic theory

“…(ii) As the perturbations are relative to the Maxwellians, which are closely related to the macroscopic state variables [21], these results perhaps verify Gatignol's comments on the general 2n-velocity model that for n 3, there are more collision invariants than physical ones or conservation laws which correspond to the number of macroscopic variables (in 2D, there are only four-i.e., one mass, two momenta, one energy). Thus there are unphysical (spurious) invariants or macroscopic variables for n 3 [21,22] which produce the essential differences between the results of from four-and six-or eight-velocity models. (iii) The diffusion mode [5,14,[24][25][26], or the related entropy wave, however, may be found to have another physical meaning once relevant measurements can be conducted.…”

“…Besides, because of the discrete nature of the four-velocity model, considering the discrete number density, our results underestimated the sound attenuation compared with those from measurements and continuous Boltzmann approaches. (ii) As the perturbations are relative to the Maxwellians, which are closely related to the macroscopic state variables [21], these results perhaps verify Gatignol's comments on the general 2n-velocity model that for n 3, there are more collision invariants than physical ones or conservation laws which correspond to the number of macroscopic variables (in 2D, there are only four-i.e., one mass, two momenta, one energy). Thus there are unphysical (spurious) invariants or macroscopic variables for n 3 [21,22] which produce the essential differences between the results of from four-and six-or eight-velocity models.…”

“…After we obtain the complex roots (λ) for the polynomial equations given above [22], we obtain the values for the (non-dimensional) sound dispersion (real part: λ i ; which is a kind of the measure of the ratio between the propagating and the reference sound speeds) and the attenuation or absorption (imaginary part: λ i ). The spectra of the (2 × n)-velocity models for n = 2, 3, 4 look entirely different [21]. To compare with previous results, we have already found the rules of transformation between different researchers' parameters, like h and the inverse Knudsen number.…”

“…The primary approach is to use the discrete velocity instead of the continuous velocity of the corresponding molecular distribution. To replace the continuous Boltzmann equation (CBE), which is required whenever the mean free path of the gas molecules is not negligible in comparison with the length scale of the problem considered, mathematical and physical aspects of the DBE were intensively investigated again in the late 1980s [21].…”

More about `On the physics of micromachines'

“…Disturbances or noises of gas flow, natural or man-made, inside microdomains could be amplified into nonlinear (evolutional) waves (for example, solitons [9]) or energies supplied to gas flow will be suddenly damped out or dissipated (damping due to solids included) by linear and/or quasi-thermal waves [9][10][11][12]. Fluctuations will frequently occur and lead to essential difficulties for MEMS and nanoelectromechanical system (NEMS) measurements or probings [7][8][9]12]. Atomic or lattice (phonon) vibrations should be taken into account once the dynamical processes on multi-critical timescales are involved in MEMS or NEMS.…”