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In South Asia and Africa, an estimated 88.5 million diarrhea episodes are attributed to Shigella infections annually (1). Shigellosis occurs most often in children < 5 years of age (2,3). [...]

The objective of this study was to assess the effectiveness of alkaline hydrolysis as an alternative ex situ technology for remediating groundwater contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Treatment in both batch reactor and continuous stirred tank reactor (CSTR) was investigated. RDX reactivity was strongly dependent on the reaction pH investigated (11-13). The batch system achieved pseudo-first-order RDX reaction rates in the range of (0.8-27.7) x [10.sup.-3] [min.sup.-1], corresponding to half-life periods of 17.9 to 0.5 h, respectively. In the CSTR system operated at the initial RDX concentration of 4.5 x [10.sup.-3] mM, 99% RDX removal was achieved with the hydraulic retention time of 2 days and the reaction pH of 11.9. Formate and nitrite were produced as the major hydrolysates in the CSTR system, indicating a simultaneous reaction mechanism involving RDX ring cleavage and elimination of the ring nitrogen. The net OH- demand used only for RDX removal in the CSTR was found to be 1.5, 390, and 130 M O[H.sup.-]/M RD[X.sub.removed] at pH values of 11.9, 11.5, and 11.0, respectively. A conceptual cost analysis indicated that the expense of alkaline treatment may be comparable to the expense of granular activated carbon treatment for long treatment periods (30 years or more), due to the potentially lower annual operational cost of alkali treatment. DOI: 10.1061/(ASCE)0733-9372(2006)132:2(256) CE Database subject headings: Alkalinity; Reactors; Costs; Water treatment; Remedial action; Ground-water pollution.

Low-pressure membranes provide high-quality water through physical removal of bacteria, cysts, and particles. Bacteria can attach to the membrane surface and form biofilms that reduce energy efficiency and increase the frequency of membrane replacement. Modifying membranes with polydopamine, a chemical mimic of the adhesive proteins that mussels release, has the potential to delay biofilm formation. Dopamine polymerizes under mild conditions, forming a coating that is of interest in membrane applications due to its hydrophilic and reactive nature. Compared with hydrophobic base membranes, hydrophilic surfaces are resistant to bacterial attachment. Additionally, when polydopamine is exposed to silver nitrate, a reduction reaction takes place that embeds antimicrobial silver nanoparticles into the polydopamine layer. This study paired short-term deposition experiments with longer-term filtration experiments to determine the efficacy of this modification when challenged with Pseudomonas aeruginosa. Modification with polydopamine resulted in an average 48% reduction in the initial deposition rate of P. aeruginosa. However, hydrophilicity of the polydopamine layer did not have a significant impact on membrane performance over 3 days of bacterial filtration. Only the combination of both polydopamine and silver nanoparticles improved the rate of water production, with an average flux 1.7 times greater than that of the unmodified membrane. Confocal microscopy revealed heterogeneous bacterial growth on all membrane types with a lack of association between membrane performance and biofilm structure. Modifying membranes with polydopamine and silver nanoparticles has the potential to ameliorate the effects of biofouling, thereby increasing the efficiency of membrane water treatment. [ABSTRACT FROM AUTHOR]

Abstract Algal-bacteria high-rate ponds represent an energy-efficient wastewater treatment approach and a source for affordable and sustainable biomass feedstock for production of renewable energy through anaerobic digestion (AD). However, there is still a need for more data on wastewater treatment efficiency, biomass productivity and settleability from outdoor treatment facilities, as well as on impact of variability in biomass composition and digestibility on methane yield and energy output. Hydraulic retention time (HRT) and wastewater quality fed into 30 m2 raceway ponds had a major effect on algal-bacteria polyculture productivity, settleability, phylogenetic and biochemical compositions, digestibility and methane yield. While Micractinium , Scenedesmus , Chlorella , and pennate diatoms were always among the key species observed, the gross productivity and 2-hour settleability during summer cultivation varied in the first-stage ponds treating primary wastewater from 29 ± 5 to 54 ± 12 g AFDW /m2/d and from 88 ± 8 to 94 ± 4% for HRT of 3 and 2 days, respectively. For these conditions, the effluent had csBOD of 3.4 or 3.3 mg/L and N total (mostly NO 3 −-N) of 9.2 or 8.2 mg/L, respectively. The second-stage algal ponds (HRT 3 days) showed lower productivity of 16 ± 6 g AFDW /m2/d, settleability of 84 ± 11%, and effluent csBOD 3.7 mg/L and N total 0.8 mg/L. Biomass composition from different ponds was 34–38% protein, 18–28% total lipids and 6–14% FAME. The methane yield varied about 30% with largest value of 0.34 ± 0.01 L/gVS and showed a positive correlation with biomass lipid content (R2 = 0.93). First-order and pseudo-parallel first-order rate kinetic models exhibited a better fit for methane production (most R2 > 0.993) than the modified Gompertz model. The variation in biomass composition led to significant differences in energy output (varied by about 60%), Net Energy Ratios (ranged from 1.6 to 2.2) and Net Energy Efficiency (from 60% to 70%) when projecting the energy balance for a large-scale continuous AD process with an optimal HRT of 20–30 days. Graphical abstract Unlabelled Image Highlights • Pond residence time (HRT) and water quality affected productivity and settleability. • 2 days HRT provided superior biomass productivity and settleability than 3 days HRT. • 1-Stage pond system provided same organic C but lower N removal than 2-stage ponds. • CH 4 yield from biomass from different ponds varied ~30% (max value 0.34 ± 0.01 L/gVS). • Net Energy Output varied by 60% and Net Energy Ration ranged from 1.6 to 2.5. [ABSTRACT FROM AUTHOR]

Scale-up of microalgal biofuel technology is challenged by availability of nitrogen and phosphorus fertilizers and the potential negative impact vast increases in chemical fertilizer demand would have on conventional agriculture. The current study investigated replacement of chemical fertilizers with nutrients sourced from primary and secondary wastewater effluents and anaerobic digestion centrate (ADC). Although primary wastewater effluent possessed a high optical density (OD) and bacterial contamination, it was a superior growth medium for microalgal cultivation than nutrient-scarce secondary effluent. Chlorella sorokiniana and Scenedesmus acutus f. alternans showed higher growth rates, productivities, and robustness than other species or poly-cultures of five species. While supplementing with 5–10% nutrient-rich ADC increased wastewater OD, it also enhanced microalgal growth rates from 0.2–0.3 d − 1 to 0.7–0.9 d − 1 and biomass productivity from 10 to 20 mg L − 1 d to 40–60 mg L − 1 d with greater improvements for secondary effluents. Supplementation with ADC also increased nutrient concentrations (N, P, Mn, B, Zn, Co by > 100% and S, Mg, Ca, Mo by 20–60%) and improved the nitrogen to phosphorus (N:P) ratio. Higher ADC dose of 20% inhibited microalgae growth potentially due to ammonia toxicity. Elevation of inoculum doses and light intensity increased final biomass density and productivity, with intensities < 140 μmol photon m − 2 s − 1 limiting algal growth rates. Inoculum doses of ≥ 2.5 × 10 5 cell mL − 1 were most favorable for cultivation of all tested microalgae and for FAME content and composition for a newly characterized strain of Chlorella sorokiniana . Overall, ADC represents an economical fertilizer substitute providing various nutrients needed for microalgal growth and enhancing biofuel sustainability. [ABSTRACT FROM AUTHOR]