Biosolids and Sludge Management.

The field of biosolids and sludge has progressed significantly over the past year. This review includes summations of the leading research published in journals and conference proceedings in 2017. The following sections are presented: biosolids regulations and management issues; biosolids characteristics, quality and measurement including microconstituents, pathogens, nanoparticles, and metals; sludge treatment technologies including pretreatment and sludge minimization, conditioning and dewatering, digestion, composting, and innovative technologies; disposal and reuse including combustion/incineration, agricultural uses, and innovative uses; odor and air emissions; and energy issues.

Mixing and Transport.

This section covers research published during the calendar year 2017 on mixing and transport processes. The review covers mixing and transport of anaerobic digesters.

Biosolids and Sludge Management.

This review covers journal articles and conference papers related to biosolids and sludge management that were published in 2016. The literature review has been divided into the following sections: •Biosolids regulations and management issues; • Biosolids characteristics, quality and measurement including microconstituents, pathogens, nanoparticles, and metals; • Sludge treatment technologies including pretreatment and sludge minimization, conditioning and dewatering, digestion, composting, and innovative technologies; • Disposal and reuse including combustion/ incineration, agricultural uses, and innovative uses; • Odor and air emissions; and • Energy issues.

Biosolids and Sludge Management.

This review section covers journal articles and conference papers related to biosolids and sludge management that were published in 2014. The literature review has been divided into the following sections: • Biosolids regulations and management issues; • ;Biosolids characteristics, quality and measurement including microconstituents and pathogens; • Sludge treatment technologies including pretreatment and sludge minimization, conditioning and dewatering, digestion, composting and innovative technologies; • Disposal and reuse including combustion/ incineration, land application and non- agricultural use; • Odor and air emissions; and • Energy issues.

Effect of total solids on fecal coliform regrowth in anaerobically digested biosolids.

Fecal coliform (FC) concentrations in anaerobically digested biosolids can increase during centrifugal dewatering and afterwards in storage of dewatered cake. The immediate increase after centrifugation (reactivation) has been demonstrated to be the revitalization of fecal coliforms that had become non-culturable. The increase during storage (regrowth) has been regarded as a subsequence of reactivated bacteria growing in a favorable environment. In this paper, however, regrowth is demonstrated without preceding reactivation, using intensive laboratory centrifugation to duplicate the levels of regrowth seen in full-scale centrifugation. Higher total solids (TS) levels of the dewatered biosolids lead to greater magnitudes of FC increase. The final TS level appears much more important than the level of shear imposed during centrifugation, based on comparison of different centrifugation/dilution procedures used to obtain similar TS levels. The greater TS levels also reduce methane production, suggesting that methanogens compete with, or inhibit, the fecal coliforms. The addition of bromoethanesulfonate as a methanogen-specific inhibitor decreased the production of methane gas, and also increased the number of fecal coliforms.

Increases in fecal coliform bacteria resulting from centrifugal dewatering of digested biosolids.

In many countries, the classification of biosolids for disposal purposes can be based, in part, on fecal coliform levels, with alternative criteria also available based on the stabilization process used, such as anaerobic digestion. The assumption that these alternative criteria provide equivalent protection may be flawed. This paper demonstrates that fecal coliform levels determined after digestion do not always indicate the bacterial levels after the same biosolids have been dewatered by centrifugation. In samples from mesophilic digestion, half had significant increases in coliform numbers (P<0.05) with up to one order of magnitude increase during centrifugation, suggesting coliform regrowth. Thermophilically digested samples had significant increases of several orders of magnitude during dewatering, more likely from reactivation of viable but non-culturable coliforms than from regrowth. In other cases, centrifugation induced coliform regrowth or reactivation upon incubation and storage of dewatered samples, but not digested samples. These 2-3 order of magnitude increases occurred with both 25 and 37 degrees C incubations. Coliform increases continued for up to 5 days, then gradually declined. However, by day 20 coliform numbers were still 2 orders of magnitude greater than when originally sampled. The magnitude of the increases could be due either to regrowth or reactivation, but the nature of the longer-term increases--also seen in biosolids/soil mixtures--suggests regrowth. Differences in numbers between digested and dewatered samples could not be duplicated with high shear processing in lab-scale devices, with nitrogen purging to remove volatile or gaseous constituents, or with redilution using centrate. They could not be attributed to enumeration methods, to interference of Bacillus spp. on apparent coliform counts, or to temperature changes. The increases have practical implications in the use of fecal coliform or alternative criteria to define pathogen content in biosolids.

Kinetics of cyanogen chloride destruction by chemical reduction methods.

In this study, membrane introduction mass spectrometry (MIMS) was applied to evaluate the kinetics of cyanogen chloride (ClCN) destruction by chemical reduction methods, using thiosulfate, sulfite, metabisulfite, ferrous ions and zero-valent iron at various concentrations and pH. The ClCN destruction followed second-order reaction kinetics in all cases of using sulfur compounds, though the second-order rate constants varied substantially from approximately 0.3-25.7 M(-1)s(-1) under different experimental conditions. The destruction of ClCN was primarily attributable to the chemical reduction pathway. Hydroxide-assisted ClCN hydrolysis was only significant at pH 9 and also when the observed reduction rate was relatively slow. The second-order rate constants achieved by sulfur(IV) compounds in the form of sulfite were found to be higher than those obtained with thiosulfate and S(IV) compounds in the form of bisulfite. Ferrous ions and zero-valent iron demonstrated slow or no ClCN reduction up to dosages of 1000 mgL(-1) and 100 gL(-1), respectively. These findings suggest that applying moderately high dosages of S(IV) compounds under neutral or alkali conditions with sufficient contact time is required for wastewater ClCN destruction. In addition, ClCN losses during long-term preservation with excess reducing sulfur compounds prior to analysis can be substantial and should be avoided.

Formation of haloacetic acids during monochloramination.

Factors that affect the formation of haloacetic acids (HAAs) during monochloramination, such as monochloramine application techniques, the initial chlorine (Cl) to ammonia-N (N) ratios, the bromide concentrations, and the wastewater quality, were studied. Aqueous humic acid solutions and undisinfected wastewater effluent samples obtained from two Hong Kong Sewage Treatment Works (STWs) were monochloraminated under various conditions. HAA formation was strongly affected by the monochloramine application techniques. The formation of trichloroacetic acid (TCAA) and total HAAs was reduced by adding preformed monochloramine. A higher initial Cl:N ratio indicated a higher chlorine demand and consequently led to higher HAA yields. Increasing the bromide concentration shifted HAAs from chlorinated species to brominated species and increased the yields of total HAAs, concurrent with decreases in the yields of dichloroacetic acid (DCAA) and TCAA but with increases in those of the other HAAs measured. Variations in the patterns of HAA formation were observed in monochloraminated wastewater effluent samples. The variations cannot be simply explained by the chlorine chemistry involving ammonia and/or bromide but are likely attributable to the combining effects of the water quality and the characteristics of the organics in the wastewater.