Improvement of COD removal by controlling the substrate degradability during the anaerobic digestion of recalcitrant wastewater

Mineral residue accelerant-enhanced anaerobic digestion of cow manure: An evaluation system of comprehensive performance

Anaerobic digestion (AD) is an efficient technology for treating biowaste and generating biogas. A reasonable evaluation of AD performance is crucial to its development. Herein, a comprehensive evaluation system covering five dimensions (energy output, process stability, degradation efficiency, digestate fertility, and digestate safety) was established to assess AD performance. Each dimension in the evaluation system was assigned a specific indicator defined by a threshold or range. Additionally, the proposed evaluation system was applied to assess a case study of batch-mode mesophilic AD that employed three industrial waste residues as mineral accelerants (nickel‑iron slag, steel slag, and fly ash). The mineral accelerants enhanced the energy output (methane yield by 66.55 %-87.54 %) and the feedstock degradation (chemical oxygen demand removal ratio by 11.23 %-32.42 %). The digestates also retained promising safety (heavy metal contents of 190-1260 mg/kg) and fertility (total nutrient contents of 3.71 %-4.69 %). The evaluation system reasonably appraised the comprehensive performance of accelerant-enhanced AD systems with cow manure. This work provides a reliable methodology for evaluating and comparing the performance of different novel accelerants and can be applied to evaluate the comprehensive performance of large-scale biogas projects with cow manure.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Review of Soft Sensors in Anaerobic Digestion Process

Anaerobic digestion is associated with various crucial variables, such as biogas yield, chemical oxygen demand, and volatile fatty acid concentration. Real-time monitoring of these variables can not only reflect the process of anaerobic digestion directly but also accelerate the efficiency of resource conversion and improve the stability of the reaction process. However, the current real-time monitoring equipment on the market cannot be widely used in the industrial production process due to its defects such as expensive equipment, low accuracy, and lagging analysis. Therefore, it is essential to conduct soft sensor modeling for unmeasurable variables and use auxiliary variables to realize real-time monitoring, optimization, and control of the an-aerobic digestion process. In this paper, the basic principle and process flow of anaerobic digestion are first briefly introduced. Subsequently, the development history of the traditional soft sensor is systematically reviewed, the latest development of soft sensors was detailed, and the obstacles of the soft sensor in the industrial production process are discussed. Finally, the future development trend of deep learning in soft sensors is deeply discussed, and future research directions are provided.

Assessment of Municipal Solid Waste Generation in Universiti Putra Malaysia and Its Potential for Green Energy Production

The global waste generation keeps increasing over the years and it requires innovative solutions to minimize its impacts on environmental quality and public health. A strategic plan must be ascertained to overcome the future challenges of Municipal solid waste (MSW) locally and globally. Universiti Putra Malaysia (UPM) coined an initiative to demonstrate a showcase pilot plant for green energy production from MSW. The data was obtained from the survey and actual sampling within the UPM compound shows that UPM has generated 5.0–7.0 t/d of MSW generated consist of 30–35% organic fraction. Restaurants are the main source of the organic fraction. Upon separation, the organic fractions were digested into biogas. At a maximum conversion of the organic fraction, 715 kWh of electricity might be generated from the 2.2 t/d of organic waste generated in UPM. In this study, organic components from UPM were proposed to be subsequently used as a substrate via anaerobic digestion to produce green energy in the form of electricity or flammable fuels.

Different bioreactors for treating secondary effluent from recycled paper mill

Secondary effluent from paper mill was characterized by poor biodegradability and containing recalcitrant compounds. In this study, four bioreactors, including a sequencing batch biofilm reactor (SBBR), a stirred-tank reactor (STR) and two submerged aeration reactors (SAR) were used to treat secondary effluent from a recycled paper mill respectively. The results indicated that chemical oxygen demand (COD) was increased by SAR2 treatment and COD removal efficiency for SBBR, SAR1 and STR was 39.7%, 15.7% and 30.9% respectively. It is suggested that recalcitrant compounds were removed by SBBR, SAR1 and STR respectively. Total nitrogen (TN) and total phosphorus (TP) of wastewater were increased by treatments of each bioreactor, which suggested that endogenous respiration of biomass occurred during the treatment. Microbial analysis of sludge from different bioreactors suggested that the removal of recalcitrant compounds in SBBR and STR might be related to the presence of unique microorganisms in each reactor.

Online prediction of effluent COD in the anaerobic wastewater treatment system based on PCA-LSSVM algorithm

Since anaerobic wastewater treatment is a nonlinear and complex biochemical process, reasonable monitoring and control are needed to keep it operating stably and efficiently. In this paper, a least-square support-vector machine (LS-SVM) was employed to construct models for the prediction of effluent chemical oxygen demand (COD) in an anaerobic wastewater treatment system. The result revealed that the performance of the steady-state model based on LS-SVM for predicting effluent COD was acceptable, with the maximum relative error (RE) of 11.45%, the mean average percentage error (MAPE) of 0.79% and the root mean square error (RMSE) of 3.08 when training, and the performance fell slightly when testing. Even though, the correlation coefficient value (R) between the predicted value and the actual value of 0.9752 could be achieved, which means this model can predict the variation of effluent COD in general. The dynamic-state models under three kinds of shock loads, which were concentration, hydraulic, and bicarbonate buffer absent, showed good forecasting performance, the correlation coefficient values (R) all excelled 0.99. Among these three shocks, the dynamic LS-SVM model under bicarbonate buffer absent shock achieved the optimal performance and followed by the dynamic-state model under hydraulic shock. This paper provides a meaningful reference to improve the monitoring level of the anaerobic wastewater treatment process.

Effect of coexisting components on phosphate adsorption using magnetite particles in water

In this study, we focused on the rate of adsorption of phosphate on to the surface of magnetite in the presence of coexisting anions, organic matters and heavy metals. Magnetite particles were prepared using a co-precipitation method. Iron (II) sulfate heptahydrate and iron (III) chloride hexahydrate were mixed and then a sodium hydroxide solution was added drop-wise in the mixed iron solution. Coexisting anions were found to have no effect on the decrease in phosphate adsorption. However, phosphate adsorbed on to magnetite surface decreased with increasing total organic carbon (TOC) concentration of natural organic matter (NOM) such as citric, oxalic, and humic acid. The amount of phosphate adsorbed rapidly decreased with the increase of NOM concentration; therefore, it can be noted that NOM concentration considerably affects the adsorption of phosphate due to the negative charge exiting on the surface of NOMs. Glucose and ethanol, meanwhile, were found to have no effect on the phosphate adsorption. The amount of phosphate adsorbed did not change in the presence of heavy metals, namely, Pb and Cd, under acidic conditions. However, under alkaline conditions, the amount of phosphate adsorbed decreased with increasing concentrations of Pb and Cd. In the case of coexisting As(III), the amount of phosphate adsorbed decreased at all pH levels with increasing As(III) concentrations.

Raw hematite based Fe(III) bio-reduction process for humified landfill leachate treatment

Microorganisms from paddy soils and raw hematite are used for enhancing natural Fe(III) bio-reduction, in order to remove macromolecular organic pollutants from humified landfill leachate. Based on batch experiments, 60% of refractory organics can be adsorbed by hematite in 12 days. In the presence of Fe(III)-reducing bacteria, 489.60 ± 0.14 mg L^-1 of dissolved organic matters can be degraded to 51.90 ± 3.96 mg L^-1 within 50 days; twelve types of semi volatile organic compounds can be degraded; hereby, the reaction follows a first-order kinetics. Crystalline Fe(III) is transformed into the amorphous form and reduced to Fe(II), hydroquinone functional groups in the humic acid (HA) are transformed to quinone ones, and the formation of HA-hematite ligands is promoted. Comparing with most of the studies about electron shuttling of HA, the transformation of quinone in the HA to hydroquinone could not be observed in the present bio-system. Based on column evaluations, more than 93% of chemical oxygen demand (influent concentration of 658 ± 19 mg L^-1) could be removed microbially under flow conditions, when the hydraulic retention time was 45 h. Raw hematite-based Fe(III) bio-reduction has a promising potential for the removal of humic and benzene series in humified landfill leachate.