Microbial community dynamics linked to enhanced substrate availability and biogas production of electrokinetically pre-treated waste activated sludge

The restricted hydrolytic degradation rate of complex organic matter presents a considerable challenge in anaerobic digestion of waste activated sludge (WAS). Within this context, application of pre-treatment of digester substrate has potential for improved waste management and enhanced biogas production. Anaerobic degradation of untreated or electrokinetically pre-treated WAS was performed in two pilot-scale digesters for 132days. WAS electrokinetically pre-treated with energy input 0.066kJ/kg sludge was used in a first phase of operation and WAS pre-treated with energy input 0.091kJ/kg sludge was used in a second phase (each phase lasted at least three hydraulic retention times). Substrate characteristics before and after pre-treatment and effects on biogas digester performance were comprehensively analysed. To gain insights into influences of altered substrate characteristics on microbial communities, the dynamics within the bacterial and archaeal communities in the two digesters were investigated using 16S rRNA gene sequencing (pyrosequencing) and quantitative PCR (qPCR). Specific primers targeting dominant operation taxonomic units (OTUs) and members of the candidate phylum Cloacimonetes were designed to further evaluate their abundance and dynamics in the digesters. Electrokinetic pre-treatment significantly improved chemical oxygen demand (COD) and carbohydrate solubility and increased biogas production by 10-11% compared with untreated sludge. Compositional similarity of the bacterial community during initial operation and diversification during later operation indicated gradual adaptation of the community to the higher solubility of organic material in the pre-treated substrate. Further analyses revealed positive correlations between gene abundance of dominant OTUs related to Clostridia and Cloacimonetes and increased substrate availability and biogas production. Among the methanogens, the genus Methanosaeta dominated in both digesters. Overall, the results showed that electrokinetic pre-treatment of WAS increases substrate solubility and biogas production. Changes in bacterial community composition and abundances of dominant bacterial OTUs were observed during anaerobic degradation of pre-treated WAS, whereas the relative abundance of methanogenic community members remained stable.publisher: Elsevier articletitle: Microbial community dynamics linked to enhanced substrate availability and biogas production of electrokinetically pre-treated waste activated sludge journaltitle: Bioresource Technology articlelink: http://dx.doi.org/10.1016/j.biortech.2016.07.029 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Decolorization of reactive azo dyes using a sequential chemical and activated sludge treatment

Textile wastewater contains high concentrations of organic substances derived from diverse dyes and auxiliary chemicals, some of which are non-biodegradable and/or toxic. Therefore, it is essential that textile wastewater is treated and that these substances are removed before being discharged into the environment. A combination of advanced oxidation processes (AOPs) to obtain partial dye degradation followed by a biological treatment has been suggested as a promising method for cost-effective decolorization of wastewater. The aim of this study was to develop and evaluate a combined method of partial Fenton's oxidation and biological treatment using activated sludge for decolorization of azo dyes, which represent an important group of recalcitrant, toxic textile dyes. Using Reactive Violet 5 (RV5) as a model dye, color removal was significantly higher when the combined Fenton treatment/activated sludge method was used, as opposed to separate application of these treatments. More specifically, pretreatment with Fenton's reagent removed 52.9, 83.9 and 91.3 % of color from a 500 mg l(-1) RV5 aqueous solution within 60 min when H2O2 concentrations of 1.0, 1.5, and 2.0 mM were used, respectively. Subsequent biological treatment was found to significantly enhance the chemical treatment, with microbial decolorization removing 70.2 % of the remaining RV5 concentration, on average. Molecular analysis of the microbial community within the activated sludge revealed that exposure to RV5 shifted the community composition from diverse towards a highly-specialized community harboring taxa with azo dye degrading activity, including Trichosporon, Aspergillus and Clostridium species.status: publishe

Assessing the composition of microbial communities in textile wastewater treatment plants in comparison with municipal wastewater treatment plants

It is assumed that microbial communities involved in the biological treatment of different wastewaters having a different chemical composition harbor different microbial populations which are specifically adapted to the environmental stresses encountered in these systems. Yet, little is known about the composition of these microbial communities. Therefore, the aim of this study was to assess the microbial community composition over two seasons (winter and summer) in activated sludge from well-operating textile wastewater treatment plants (WWTPs) in comparison with municipal WWTPs, and to explain observed differences by environmental variables. 454-pyrosequencing generated 160 archaeal and 1645 bacterial species-level Operational Taxonomic Units (OTUs), with lower observed richness in activated sludge from textile WWTPs compared to municipal WWTPs. The bacterial phyla Planctomycetes, Chloroflexi, Chlorobi, and Acidobacteria were more abundant in activated sludge samples from textile WWTPs, together with archaeal members of Thaumarchaeota. Nonmetric multidimensional scaling analysis of the microbial communities showed that microbial communities from textile and municipal WWTPs were significantly different, with a seasonal effect on archaea. Nitrifying and denitrifying bacteria as well as phosphate-accumulation bacteria were more abundant in municipal WWTPs, while sulfate-reducing bacteria were almost only detected in textile WWTPs. Additionally, microbial communities from textile WWTPs were more dissimilar than those of municipal WWTPs, possibly due to a wider diversity in environmental stresses to which microbial communities in textile WWTPs are subjected to. High salinity, high organic loads, and a higher water temperature were important potential variables driving the microbial community composition in textile WWTPs. This study provides a general view on the composition of microbial communities in activated sludge of textile WWTPs, and may provide novel insights for identifying key players performing important functions in the purification of textile wastewaters.First published: 25 September 2016status: publishe

Nitrification and microalgae cultivation for two-stage biological nutrient valorization from source separated urine

Urine contains the majority of nutrients in urban wastewaters and is an ideal nutrient recovery target. In this study, stabilization of real undiluted urine through nitrification and subsequent microalgae cultivation were explored as strategy for biological nutrient recovery. A nitrifying inoculum screening revealed a commercial aquaculture inoculum to have the highest halotolerance. This inoculum was compared with municipal activated sludge for the start-up of two nitrification membrane bioreactors. Complete nitrification of undiluted urine was achieved in both systems at a conductivity of 75mScm(-1) and loading rate above 450mgNL(-1)d(-1). The halotolerant inoculum shortened the start-up time with 54%. Nitrite oxidizers showed faster salt adaptation and Nitrobacter spp. became the dominant nitrite oxidizers. Nitrified urine as growth medium for Arthrospira platensis demonstrated superior growth compared to untreated urine and resulted in a high protein content of 62%. This two-stage strategy is therefore a promising approach for biological nutrient recovery.publisher: Elsevier articletitle: Nitrification and microalgae cultivation for two-stage biological nutrient valorization from source separated urine journaltitle: Bioresource Technology articlelink: http://dx.doi.org/10.1016/j.biortech.2016.03.001 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Empowering a mesophilic inoculum for thermophilic nitrification: Growth mode and temperature pattern as critical proliferation factors for archaeal ammonia oxidizers

Cost-efficient biological treatment of warm nitrogenous wastewaters requires the development of thermophilic nitrogen removal processes. Only one thermophilic nitrifying bioreactor was described so far, achieving 200 mg N L(-1) d(-1) after more than 300 days of enrichment from compost samples. From the practical point of view in which existing plants would be upgraded, however, a more time-efficient development strategy based on mesophilic nitrifying sludge is preferred. This study evaluated the adaptive capacities of mesophilic nitrifying sludge for two linear temperature increase patterns (non-oscillating vs. oscillating), two different slopes (0.25 vs. 0.08 °C d(-1)) and two different reactor types (floc vs. biofilm growth). The oscillating temperature pattern (0.25 °C d(-1)) and the moving bed biofilm reactor (0.08 °C d(-1)) could not reach nitrification at temperatures higher than 46 °C. However, nitrification rates up to 800 mg N L(-1) d(-1) and 150 mg N g(-1) volatile suspended solids d(-1) were achieved at a temperature as high as 49 °C by imposing the slowest linear temperature increase to floccular sludge. Microbial community analysis revealed that this successful transition was related with a shift in ammonium oxidizing archaea dominating ammonia oxidizing bacteria, while for nitrite oxidation Nitrospira spp. was constantly more abundant than Nitrobacter spp.. This observation was accompanied with an increase in observed sludge yield and a shift in maximal optimum temperature, determined with ex-situ temperature sensitivity measurements, predicting an upcoming reactor failure at higher temperature. Overall, this study achieved nitrification at 49 °C within 150 days by gradual adaptation of mesophilic sludge, and showed that ex-situ temperature sensitivity screening can be used to monitor and steer the transition process.publisher: Elsevier articletitle: Empowering a mesophilic inoculum for thermophilic nitrification: Growth mode and temperature pattern as critical proliferation factors for archaeal ammonia oxidizers journaltitle: Water Research articlelink: http://dx.doi.org/10.1016/j.watres.2016.01.022 content_type: article copyright: Copyright © 2016 Elsevier Ltd. All rights reserved.status: publishe

Empowering a mesophilic inoculum for thermophilic nitrification: Growth mode and temperature pattern as critical proliferation factors for archaeal ammonia oxidizers.

Cost-efficient biological treatment of warm nitrogenous wastewaters requires the development of thermophilic nitrogen removal processes. Only one thermophilic nitrifying bioreactor was described so far, achieving 200 mg N L(-1) d(-1) after more than 300 days of enrichment from compost samples. From the practical point of view in which existing plants would be upgraded, however, a more time-efficient development strategy based on mesophilic nitrifying sludge is preferred. This study evaluated the adaptive capacities of mesophilic nitrifying sludge for two linear temperature increase patterns (non-oscillating vs. oscillating), two different slopes (0.25 vs. 0.08 °C d(-1)) and two different reactor types (floc vs. biofilm growth). The oscillating temperature pattern (0.25 °C d(-1)) and the moving bed biofilm reactor (0.08 °C d(-1)) could not reach nitrification at temperatures higher than 46 °C. However, nitrification rates up to 800 mg N L(-1) d(-1) and 150 mg N g(-1) volatile suspended solids d(-1) were achieved at a temperature as high as 49 °C by imposing the slowest linear temperature increase to floccular sludge. Microbial community analysis revealed that this successful transition was related with a shift in ammonium oxidizing archaea dominating ammonia oxidizing bacteria, while for nitrite oxidation Nitrospira spp. was constantly more abundant than Nitrobacter spp.. This observation was accompanied with an increase in observed sludge yield and a shift in maximal optimum temperature, determined with ex-situ temperature sensitivity measurements, predicting an upcoming reactor failure at higher temperature. Overall, this study achieved nitrification at 49 °C within 150 days by gradual adaptation of mesophilic sludge, and showed that ex-situ temperature sensitivity screening can be used to monitor and steer the transition process