Enhanced Sludge Dewatering Research Articles

Enhancing pulp and paper mill biosludge dewaterability using enzymes

There have been limited studies on the potential use of enzymes for enhancing the dewaterability of biosludge. The mechanisms for such enhancement have not been investigated despite the environmental advantages of using enzymes over synthetic polymers for biosludge conditioning. In order to find enzymes with this potential, a screening of commercially available enzymes was carried out using capillary suction time to assess biosludge dewaterability. The only enzyme that showed dewatering improvements in the screening tests was a lysozyme which reduced the capillary suction time by 36% and increased the cake solids content from 5.6 to 8.9 DS%. Lysozyme aided in the flocculation of particles reducing the polymer demand from 11% to 6%. Active and inactive lysozyme exhibited a similar ability for enhancing sludge dewatering, indicating that the conditioning mechanism of lysozyme is similar to that of a flocculant.

Enhanced Sludge Dewatering Performance by a Novel Bioflocculant Conditioning

The characterization and use in sludge dewatering of a novel bioflocculant M-C11 produced by Klebsiella pneumoniae was investigated. The purified M-C11 was composed of 91.20% sugar, 4.61% protein and 3.91% nucleic acids (w/w). Fourier transform infrared (FT-IR) spectroscopy of purified M-C11 confirmed the presence of carboxyl, hydroxyl, methoxyl and amino groups. The sludge resistance to filtration (SRF) decreased remarkably from 11.64×1012 m/kg to 4.66×1012 m/kg under the optimum conditions (pH=6, 3 mL bioflocculant and 4 mL CaCl2 dosage), after being conditioned with bioflocculant M-C11, which was more efficient than inorganic flocculants. Results showed that M-C11 could serve as a substitute for chemical conditioners and a promising alternative to the sludge treatment industries.

Dewatering model for optimal operation of sludge treatment wetlands

Sludge treatment wetlands (STW) are used as a dewatering technology in some European countries since the 80’s. Although the efficiency of this technology in terms of sludge dewatering and mineralisation is well known, design and operation parameters are yet to be standardised. The aim of this study is to develop a mathematical model capable of predicting the water loss with time, in order to optimise the feeding frequency enhancing sludge dewatering and expanding the lifespan of the system. The proposed model is validated with experimental data from one pilot and two full-scale STW. The scenarios considered indicate that the optimum feeding frequency decreases with the sludge layer height. In this way, systems with a sludge layer of 20 cm, 40 cm and 80 cm (corresponding to 2, 4 and 8 years of operation), should be fed every 2.5, 10 and 30–40 days, respectively. On the other hand, evapotranspiration (ET) has no effect on the feeding frequency, although it does increase the sludge dryness from 25% to 45% (for ET of 2.5 and 14.5 mm/d in the case of 20 cm of sludge height). According to the model output, the sludge loading rate is determined as a function of evapotranspiration, feeding frequency and sludge height.

Enhanced sludge dewatering by dual polyelectrolytes conditioning

Sludge dewatering by dual polyelectrolytes conditioning was investigated in this study. Single polyelectrolyte is utilized in sludge conditioning conventionally, in which charge neutralization and bridging are involved in the reactions. In the current study, both cationic and non-ionic polyelectrolytes were utilized simultaneously in the conditioning. Waste activated sludge was sampled from a synthetic fiber plant, and used in the experiment. Capillary suction time (CST), specific resistance to filtration (SRF), and settling rate were used to evaluate the sludge dewatering behaviors. Zeta potentials were also measured. Sludge dewatering behaviors resulting from single and dual polyelectrolytes conditioning were compared. It was found that sludge conditioned with dual polyelectrolytes performed better in fine particle capture and in the formation of larger flocs that resulted in a better dewaterability and less chance of overdosing. The dosing sequence in dual polyelectrolytes also affected the sludge dewaterability. Reaction mechanisms in dual polyelectrolyte conditioning were proposed based on enhanced flocculation of sludge particles.

Evaluation of effective conditioners for enhancing sludge dewatering and subsequent detachment from filter cloth

Various types of materials (including ferric chloride, alum, polymers, acids, wood chips, wheat dregs, diatomite, and coal ash) were used individually to condition a digested sludge from a brewery to investigate how adding these materials affected the dewaterability and adhesion of the sludge. Specific resistance (SR) to filtration, as an index of sludge dewaterability, and the mass of residue (MR) on the filter cloth after cake detachment, as an index of sludge adhesion, were measured to evaluate the effectiveness of conditioners. Among these additives, ferric chloride, alum, commercial organic polymers, and acids proved to be effective chemicals in reducing SR. However, only ferric chloride addition effectively decreased sludge adhesion. The optimum dosage of ferric chloride is around 15%, based on the original dry solids content of the sludge. Wood chips and wheat dregs were verified as suitable physical conditioners for both improving dewaterability and also reducing adhesion of sludge. These two inert materials also satisfy the requirements that conditioners be biodegradable, easy to obtain, and low cost, to maintain the potential utilization value of the resulting sludge cake.

Sludge Freezing in Shallow Layers

The effect of freeze-thaw conditioning for enhanced sludge dewatering is effective only when sludge freezes completely and slowly. This recognition has inhibited the development of commercialized freeze-thaw conditioners. If sludge is frozen in thin layers, however, the freezing can be slow, complete, and fairly rapid. The studies reported here suggest that the freezing rate can be assumed to be only a function of the temperature and the convection coefficient, and that the insulating effect of the ice can be ignored.