Effects of physico-chemical post-treatments on the semi-continuous anaerobic digestion of sewage sludge

Sludge production in wastewater treatment plants is increasing worldwide due to the increasing population. This work investigated the effects of ultrasonic (ULS), ultrasonic-ozone (ULS-Ozone) and ultrasonic + alkaline (ULS+ALK) post-treatments on the anaerobic digestion of sewage sludge in semi-continuous anaerobic reactors. Three conditions were tested with different hydraulic retention times (HRT, 10 or 20 days) and sludge recycle ratios (R = QR/Qin (%): 50 or 100%). Biogas yield increased by 17.8% when ULS+ALK post-treatment was applied to the effluent of a reactor operating at 20 days HRT and at a 100% recycle ratio. Operation at 10 days HRT also improved the biogas yield (277 mL CH4/g VSadded (VS: volatile solids) versus 249 mL CH4/g VSadded in the control). The tested post-treatment methods showed 4–7% decrease in effluent VS. The post-treatment resulted in a decrease in the cellular ATP (Adenosine tri-phosphate) concentration indicating stress imposed on microorganisms in the reactor. Nevertheless, this did not prevent higher biogas production. Based on the results, the post-treatment of digested sludge or treating the sludge between two digesters is an interesting alternative to pre-treatments

Effects of physico-chemical post-treatments on the semi-continuous anaerobic digestion of sewage sludge

Sludge production in wastewater treatment plants is increasing worldwide due to the increasing population. This work investigated the effects of ultrasonic (ULS), ultrasonic-ozone (ULS-Ozone) and ultrasonic + alkaline (ULS+ALK) post-treatments on the anaerobic digestion of sewage sludge in semi-continuous anaerobic reactors. Three conditions were tested with different hydraulic retention times (HRT, 10 or 20 days) and sludge recycle ratios (R = QR/Qin (%): 50 or 100%). Biogas yield increased by 17.8% when ULS+ALK post-treatment was applied to the effluent of a reactor operating at 20 days HRT and at a 100% recycle ratio. Operation at 10 days HRT also improved the biogas yield (277 mL CH4/g VSadded (VS: volatile solids) versus 249 mL CH4/g VSadded in the control). The tested post-treatment methods showed 4–7% decrease in effluent VS. The post-treatment resulted in a decrease in the cellular ATP (Adenosine tri-phosphate) concentration indicating stress imposed on microorganisms in the reactor. Nevertheless, this did not prevent higher biogas production. Based on the results, the post-treatment of digested sludge or treating the sludge between two digesters is an interesting alternative to pre-treatments

Optimizing the synergistic effect of sodium hydroxide/ultrasound pre-treatment of sludge

Ultrasound (ULS), sodium hydroxide (NaOH) and combined ultrasound/NaOH pre-treatment were applied to pre-treat waste activated sludge and improve the subsequent anaerobic digestion. Synergistic effect was observed when NaOH treatment was coupled with ultrasound treatment. The highest synergistic Chemical Oxygen Demand (COD) solubilization was observed when 0.02M NaOH was combined with five minutes ultrasonication: an extra 3,000 mg/L was achieved on top of the NaOH (1,975 mg/L) and ultrasonication (2,900 mg/L) treatment alone. Further increase of NaOH dosage increased Soluble Chemical Oxygen Demand (SCOD), but did not increase the synergistic effect. Nine minutes and 18 minutes ultrasonication led to 20% and 24% increase of methane production, respectively; Whereas, 0.05M NaOH pre-treatment did not improve the sludge biodegradability. Combined ultrasound/NaOH (9min+0.05M) showed 31% increase of methane production. A stepwise NaOH addition/ultrasound pre-treatment (0.02M+ULS for 5 min + 0.02M+ULS for 4 min) was tested and resulted in 40% increase of methane production using 20% less chemicals

Enhancing sewage sludge anaerobic 're-digestion' with combinations of ultrasonic, ozone and alkaline treatments

This study investigated the feasibility of using ultrasonic (ULS), ozone assisted ultrasonic (ULS-Ozone) and alkaline assisted ultrasonic (ULS+ALK) post-treatment to target the persistent organic fraction in anaerobically digested sludge in order to increase methane recovery. Synergistic COD solubilization in digested sludge was observed when ozone (0.012 g O3 g-1 TS) and alkaline (0.02M for 10 min.) treatment was combined with ULS treatment. The digested sludge Soluble Chemical Oxygen Demand (SCOD) increased from 200 mg/L to 1,500, 2,600 and 2,650 mg/L after the ULS, ULS-Ozone and ULS+ALK treatments, respectively. Different compounds were, however, solubilized after the ULS-Ozone and ULS+ALK treatments as indicated by size exclusion chromatography (SEC). ULS+ALK treatment primarily solubilized macromolecules with molecular weight (MW) over 500 kDa; while, the ULS-Ozone treatment solubilized macromolecules with MW higher than 500 kDa and also organics with MW around 103 kDa. The methane production from “re-digestion” of the treated digested sludge increased by 28.3%, 48.3% and 39.5% after the ULS, ULS-Ozone and ULS+ALK treatments, respectively

Study on Photon Transport Problem Based on the Platform of Molecular Optical Simulation Environment

As an important molecular imaging modality, optical imaging has attracted increasing attention in the recent years. Since the physical experiment is usually complicated and expensive, research methods based on simulation platforms have obtained extensive attention. We developed a simulation platform named Molecular Optical Simulation Environment (MOSE) to simulate photon transport in both biological tissues and free space for optical imaging based on noncontact measurement. In this platform, Monte Carlo (MC) method and the hybrid radiosity-radiance theorem are used to simulate photon transport in biological tissues and free space, respectively, so both contact and noncontact measurement modes of optical imaging can be simulated properly. In addition, a parallelization strategy for MC method is employed to improve the computational efficiency. In this paper, we study the photon transport problems in both biological tissues and free space using MOSE. The results are compared with Tracepro, simplified spherical harmonics method (SPn), and physical measurement to verify the performance of our study method on both accuracy and efficiency

Qualitative Simulation of Photon Transport in Free Space Based on Monte Carlo Method and Its Parallel Implementation

During the past decade, Monte Carlo method has obtained wide applications in optical imaging to simulate photon transport process inside tissues. However, this method has not been effectively extended to the simulation of free-space photon transport at present. In this paper, a uniform framework for noncontact optical imaging is proposed based on Monte Carlo method, which consists of the simulation of photon transport both in tissues and in free space. Specifically, the simplification theory of lens system is utilized to model the camera lens equipped in the optical imaging system, and Monte Carlo method is employed to describe the energy transformation from the tissue surface to the CCD camera. Also, the focusing effect of camera lens is considered to establish the relationship of corresponding points between tissue surface and CCD camera. Furthermore, a parallel version of the framework is realized, making the simulation much more convenient and effective. The feasibility of the uniform framework and the effectiveness of the parallel version are demonstrated with a cylindrical phantom based on real experimental results

Targeted insertion of regulatory elements enables translational enhancement in rice

In-locus editing of agronomically-important genes to optimize their spatiotemporal expression is becoming an important breeding approach. Compared to intensive studies on mRNA transcription, manipulating protein translation by genome editing has not been well exploited. Here, we found that precise knock-in of a regulating element into the 5’UTR of a target gene could efficiently increase its protein abundance in rice. We firstly screened a translational enhancer (AMVE) from alfalfa mosaic virus using protoplast-based luciferase assays with an 8.5-folds enhancement. Then the chemically modified donor of AMVE was synthesized and targeted inserted into the 5’UTRs of two genes (WRKY71 and SKC1) using CRISPR/Cas9. Following the in-locus AMVE knock-in, we observed up to a 2.8-fold increase in the amount of WRKY71 protein. Notably, editing of SKC1, a sodium transporter, significantly increased salt tolerance in T2 seedlings, indicating the expected regulation of AMVE knock-in. These data demonstrated the feasibility of such in-locus editing to enhance protein expression, providing a new approach to manipulating protein translation for crop breeding

Effects of chemically assisted ultrasonication treatments on anaerobic digestion of sewage sludge

Sewage sludge is a problematic by-product of wastewater treatment. Due to the high organic and pathogenic content, it needs to be stabilized before safe disposal. Anaerobic digestion is generally applied to stabilize sewage sludge, because it not only reduces the organic content in sludge but also generates biogas which can be used for energy supply. However, anaerobic sludge digestion is a time-consuming process because hydrolysis of particulate organics in sludge limits the overall anaerobic digestion rate. Sludge treatment is often integrated with an anaerobic digester to solubilize the solids as well as to enhance the overall anaerobic digestion performance. Sludge treatment can be integrated in two different configurations. It can be applied to feed sludge before anaerobic digestion as pre-treatment. Alternatively, it can be achieved by treating the digested sludge after anaerobic digestion and recycling the treated digested sludge to the original reactor, which is known as post-treatment. In this study, the effects of individual ultrasonication (ULS), sequentially combined ULS and ozonation (ULS-Ozone) and simultaneously combined ULS and alkaline (ULS+ALK) treatments on feed sewage sludge (i.e. pre-treatment) and digested sludge (i.e. post-treatment) were investigated. ULS pre-treatment showed limited performance in solubilizing feed sewage sludge and increasing the sludge biodegradability because it is essentially “single” effect - mechanical disintegration. Synergistic VSS solubilization was observed in feed sludge after the ULS-Ozone pre-treatment. In addition, some of the organics solubilized by ultrasound can be further broken down by ozone, resulting in solubilization of low molecular weight (MW) components (MW < 27 kDa). The ULS+ALK pre-treatment not only induced synergistic COD solubilization but also generated smaller organics with MW around 5.6 kDa in feed sludge. The biogas production increase following anaerobic digestion of ULS, ULS-Ozone, ULS+ALK treated feed sludge with semi-continuous anaerobic reactors were 20.7%, 35.5% and 24.6%, respectively at SRT of 10 days. ULS-Ozone and ULS+ALK post-treatments were found to result in synergistic COD solubilization in digested sludge. Despite the similar extent of COD solubilization (from 200 mg/L to around 2,600 mg/L), the solubilization products were different after the ULS-Ozone and ULS+ALK treatments of digested sludge. The ULS+ALK treatment of digested sludge primarily solubilized macromolecules with MW over 500 kDa. However, the ULS-Ozone treatment of digested sludge not only solubilized macromolecules with MW higher than 500 kDa but also released organics with MW around 103 kDa. The biogas production from the semi-continuous anaerobic digesters increased by 9.8%, 10.7%, 17.8% after the ULS, ULS-Ozone and ULS+ALK treated digested sludge were recycled to the anaerobic digester, respectively at SRT of 20 days and recycle ratio of 5%.Doctor of Philosoph