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Paper mill sludge (PMS) raises critical environmental issues due to its disposal problem, but its high sugar content and well-dispersed structure make it a great feedstock for biochemical production. The technical feasibility of integrating cellulase enzyme production into lactic acid (LA) fermentation from PMS was investigated in this study. The low ash content of PMS suggests a great potential for cellulase production. The enzyme produced using PMS without any treatment gave an activity of 7.8 FPU/ml, a performance comparable to the commercial enzyme, Cellic CTec 2. The LA yield from PMS with in-house enzyme was 64.7% and 73.7% at the enzyme loading of 10 and 15 FPU/g-glucan, respectively. The LA obtained was optically pure L- isomer with over 99% purity. The optimal condition of LA production by Bacillus coagulans was found to be 50 °C and pH 5.3 (with 50 g/L CaCO 3 ). The nutrient effect of yeast extract (YE) and corn steep liquor (CSL) was substrate dependent, and CSL could substitute YE as an inexpensive nutrient when using PMS as a substrate., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Sewage fine sieved fraction (FSF) is a heterogeneous substrate consisting of mainly toilet paper fibers sequestered from municipal raw sewage by a fine screen. In earlier studies, a maximum biodegradation of 62% and 57% of the sewage FSF was found under thermophilic (55°C) and mesophilic (35°C) conditions, respectively. In order to research this limited biodegradability of sewage FSF, this study investigates the biodegradation of different types of cellulosic fibers-based hygiene papers including virgin fibers based toilet paper (VTP), recycled fiber based toilet paper (RTP), virgin pulp for paper production (VPPP) as a raw material, as well as microcrystalline cellulose (MCC) as a kind of fiberless reference material. The anaerobic biodegradation or digestibility tests were conducted under thermophilic and mesophilic conditions. Results of the experiments showed different biomethane potential (BMP) values for each tested cellulose fiber-based substrate, which might be associated with the physical characteristics of the fibers, type of pulping, presence of lignin encrusted fibers, and/or the presence of additive chemicals and refractory compounds. Higher hydrolysis rates (Kh), higher specific methane production rates (SMPR) and shorter required incubation times to achieve 90% of the BMP (t90%CH4), were achieved under thermophilic conditions for all examined substrates compared to the mesophilic ones. Furthermore, the biodegradability of all employed cellulose fiber-based substrates was in the same range, 38-45%, under both conditions and less than the observed FSF biodegradability, i.e. 57-62%. MCC achieved the highest BMP and biodegradability, 86-91%, among all cellulosic substrates., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Cyclodextrins (CDs) increase the cake solids and drainage rate of belt-pressed biological or primary sludge when added to the sludge slurry along with conventional conditioning chemicals. These benefits are obtained at very low CD dosage. A 2.8 percentage point increase in cake solids was obtained in a full-scale trial with mixed primary and biological sludge from a paper mill. CDs also decrease the specific resistance to filtration and increase the capture rate of solids during belt pressing. Mechanistic studies showed that CDs increase the surface tension of c-PAM polymers in water and reduce the turbidity, indicating that they are able to aggregate the charged polymers, and, by inference, sludge particles treated with the polymer. A mechanism is proposed where CDs reduce excessively charged regions of the polymer-treated surface of the sludge, thereby facilitating its flocculation.

Subjecting a suspension of biological sludge to underwater sparks (3kV, 50kA) leads to its consolidation, decreases the charge density on the solids, and increases its settling rate. The cake solids increase, but by only one percentage point. High-speed video images show that the spark generates a steam bubble. The dynamics of bubble growth could be estimated through the Rayleigh model. The bubble collapses into an acoustic field, which then agglomerates the particles. Sparking does not affect the settling rate of an aqueous slurry of softwood pulp because the fibrous particles are too large to be aggregated by an acoustic pulse.

Twelve independent batch experiments (<9h) with fresh municipal activated sludge were conducted to assess the occurrence and the mechanisms of deflocculation under a temperature shift from 30 to 45 degrees C. In each experiment, a transient reactor (2 L) was subjected to the temperature shift and a control reactor was operated at a constant temperature of 30 degrees C. The occurrence of deflocculation was demonstrated by the increase in turbidity and in the concentrations of biopolymers in the sludge supernatant from the transient reactor. The maximum levels of proteins in the supernatants ranged from 53 to 81 mg/L, for DNA from 34 to 36 mg/L, for humic compounds from 20 to 40 mg/L, and for carbohydrates from 21 to 31 mg/L. All the biopolymer concentrations in the control reactor remained below 5-10 mg/L. The release of biopolymers was accompanied by an increase in sludge supernatant conductivity (16-32% increase, up to 1.20 mS/cm), soluble chemical oxygen demand (from 129 to 440 mg/L), total suspended solids (>25 mg/L up to 128 mg/L), and a decrease in the mixed liquor volatile suspended solids (up to 11%). The temperature shift was also found to inhibit microbial metabolism by reducing the sludge biomass substrate removal capacity, as measured by oxygen-uptake rates. The temperature shift had a marginal effect causing sludge lysis (as an increase in beta-galactosidase activity) and had no significant impact on sludge viability (live/dead ratio of bacterial cells). It was concluded that sludge deflocculation under a temperature shift from 30 to 45 degrees C involves the solubilisation of extracellular polymeric substances from the flocs and likely also floc fragmentation. In addition, sludge deflocculation and the inhibition of microbial metabolism explain the poor treatment performance observed in previous continuous reactors under similar temperature shifts.

A set of four assays designed to rapidly measure the health and biodegradative performance of pulp and paper mill activated sludges was developed. Three of the assays are specific oxygen uptake rates (SOURs) that measure the normal "working" aeration tank BOD (biochemical oxygen demand) removal rate (SOURAT), a near-maximum BOD removal rate (SOURNMAX), and a rate (SOURTOX) used in combination with the SOURNMAX to indicate the presence of toxic or inhibitory substances. The fourth assay is the specific adenosine triphosphate (SATP) content of the sludge, used as a measure of its viable cell content. Fresh biomass (sludge) samples from one laboratory reactor and four mill biotreatment systems were fed raw mill effluents and used to evaluate the four-assay set. The SOURAT values of all systems were 10-40% of their SOURNMAX values: thus the SOURAT:SOURNMAX ratios indicate that each system's free biodegradative capacity was far greater than its operating rate. It was demonstrated using phenol that the SOURNMAX:SOURTOX ratio can indicate the presence of substances toxic or inhibitory to the biomass. The results also indicated that the SOURNMAX is a much better indicator of improving or worsening sludge performance and capacity than the SOURAT. SATP was shown to be a useful monitor of the proportion of viable cells in an activated sludge and a toxicity indicator complementary to the SOURNMAX:SOURTOX ratio and similar in principle to the commercial Microtox toxicity test. This four-assay set was also applied to three practical situations: (a) at-mill monitoring of a biotreatment system; (b) effects of cold storage on biomass; and (c) effects of decreased BOD loading on biomass.