Pilot-scale Experimental Results Research Articles

A pilot study on recovery of iron from sulfur-bearing hematite ore using hydrogen-based mineral phase transformation followed by magnetic separation

Sulfur is a harmful impurity in iron ore, which seriously affects the subsequent smelting process and product quality. In this study, a novel process of hydrogen-based mineral phase transformation followed by magnetic separation was proposed to treat sulfur-bearing refractory iron ore. The results of pilot-scale experiments showed that in the oxidation heating stage, the sulfur element in the ore was oxidized to form SO2. During the reduction roasting stage, the hematite within iron ore powder was almost entirely transformed into magnetite at a reduction temperature of 520 °C using a gas combination of 45 % H2- 15 % CO- 40 % N2, which significantly enhanced the magnetism of the particles. At this time, iron minerals could be effectively recovered by a grinding and low-intensity magnetic separation process. Under the optimum roasting and magnetic separation conditions, the iron grade of magnetic concentrate reached 66.40 %, the iron recovery was 92.44 %, and the sulfur content decreased significantly from 0.547 % to 0.038 %. The hydrogen-based mineral phase transformation technology showed unique technical advantages and environmental potential in treating sulfur-bearing refractory iron ores.

Techno-economic analysis of microalgae production for aquafeed in Norway

The sustainability of the aquaculture sector depends mainly on the search for alternative sources to fishmeal and fish oil, one of which is microalgae. However, there are few feasibility studies of the microalgae process chain. This work aimed to address this gap through a TEA of microalgae (Phaeodactylum tricornutum) production. The TEA combines process modelling, engineering design and economic evaluation. As a result, different projections are obtained, yielding the breakdown of capital investment and operating costs.The study is based on pilot-scale experimental results using tubular PBR in Norway. This TEA shows that 29.48 t of biomass per ha of facility and year would be a real productivity. At PBR scales of 1 and 100 ha, microalgae could be produced for 108.26 or 44 €/kg DW of harvested biomass respectively. Artificial light is indispensable for microalgae production in Norway, as its absence would represent a 50% lower productivity and a cost increase of 95%. Producing the final product as a powder represents a 1.20% greater cost. Not only does the production under more favourable climatic conditions (southern Spain) removes the need for artificial lights and greenhouses, but it also would imply greater productivity (39.02 t/ha/year) and a reduced cost (23.08 €/kg DW of disrupted and dry biomass) at a scale of 100 ha.The main factor affecting CAPEX is the PBR, which range from 49.48 to 96.37% of the MEC. As for OPEX, the most critical elements vary with the projection: labour, energy, utilities, and other costs. The competitiveness of microalgae for aquaculture depends on a combination of different factors. Reducing the cost of the PBR and greenhouse, increasing the PE and widening the temperature range of the culture could reduce the cost by a further 76%.

Industrial application of swirl regenerating micro-channel separation (SRMS) for fine catalysts removal from methanol-to-olefin quench water

Methanol to olefin (MTO) process is a chemical technology for producing low-carbon olefins from coal-based or natural gas-based methanol, which has changed the pattern of low-carbon olefins relying on petroleum cracking. However, a large amount of fine catalyst powders circulating in the water system of the MTO plant threats the sustainability of the process severely. Previously, a pilot-scale study about swirl regenerating micro-channel separation (SRMS) technology to remove the fine waste catalyst powders from MTO quench water was reported. In this study, the SRMS equipment was scaled up to an industrial level with a processing capacity of 400 m3/h based on the results of pilot-scale experiments, and the performance of the industrial unit was monitored for over 6 months. The results obtained directly from the industrial site showed that the SRMS unit based on deep-bed filtration and swirling flow enhanced washing and desorption could effectively remove the fine catalyst particles in the quench water, and the effluent particle concentration was maintained below 20 mg/L. Furthermore, the total oil content in the quench water reduced from 43.2 mg/L to 22.8 mg/L after being processed by the SRMS unit, which demonstrates that the SRMS unit also has an appreciable ability for oil pollutants removal. After the long-term operation of the SRMS unit, the equilibrium concentration of particulate matter in the quench water was reduced to under 50 mg/L, which significantly improved the performance of the quench water heat exchanger and effectively reduced the cleaning frequency of the heat exchanger, air cooler, and other equipment in the water system. Through the industrial-scale technical comparison, this technology outperforms the other common quench water treatment methods in equipment investment, maintaining cost, freshwater supplement, and energy consumption.

Comparative study on washing effects of different washing agents and conditions on heavy metal contaminated soil

The soil washing technology of heavy metals in soil has the prospect of practical application. In this study, we screening out the best washing conditions for remediation of heavy metal contaminated soil and the conclusions are verified by pilot-scale field tests. Compared with citric acid (CA) and ethylene diamine teraacetic acid disodium salt (EDTA), Iron-based compounds (IC) has highest removal rate of heavy metals in soil. Heavy metals are mainly concentrated in soil with small particle size. Comprehensive cost consideration, the best washing concentration is 0.06 mol·L−1, the best solid liquid ratio is 1:5 and the best washing time is 30 min. CaO can precipitate heavy metals in washing waste liquor by increasing the pH of heavy metals in washing waste liquor, and the best precipitation time is 30 min considering the comprehensive cost. The results of pilot scale experiments show that the IC washing technology was shown to be an effective approach to rapidly reduce the Pb, Zn and As in contaminated soil.

Recirculation of reject water in deep-dewatering process to influent of wastewater treatment plant and dewaterability of sludge conditioned with Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8: From bench to pilot-scale study

Deep dewatering of sewage sludge pretreated with advanced oxidation processes (AOPs) is a strategy for efficient sludge reduction and subsequent disposal. The pretreatment and dewatering performance of sludge conditioned with three types of AOPs (Fe2+/H2O2, Fe2+/Ca(ClO)2, and Fe2+/Na2S2O8), compared with sludge conditioned with traditional conditioner (Fe3+/CaO), were investigated in both bench and pilot-scale tests. All of those conditioner systems could reduce the water content of dewatered sludge cake to below 60 wt% in bench-scale (about 16 kg raw sludge per round) and pilot-scale (approximate 800 kg raw sludge per round) diaphragm filter press dewatering. Compared with raw sludge, the deep-dewatering filtrate after different conditioning and dewatering processes had higher ammonia nitrogen (NH4+-N) and chemical oxygen demand (COD) contents due to the degradation of organic matter, and much lower total phosphorus (TP) content due to the formation of iron phosphate precipitate. A better biodegradability (i.e. higher BOD5/COD ratio) was found in the deep-dewatering filtrate of sludge conditioned with Fe2+/H2O2 (25.2 %) and Fe2+/Ca(ClO)2 (17.4 %). Most of the heavy metals (Cr, Cu, Ni, and Pb) (>79 wt%) have remained in the dewatered sludge cake, and most of the Cl element (>90 wt%) in the sludge pretreated by Fe2+/Ca(ClO)2 and Fe3+/CaO was kept in the filtrate, rather than the dewatered sludge cake. Based on the pilot-scale experimental results, if all the filtrate in the deep-dewatering process returned to the influent of WWTP, the loading ratios of TP, NH4+-N, COD in the four conditioner systems were less than 3 wt%. The above results proved that the AOPs conditioned sludge could achieve deep-dewatering in pilot-scale and the direct recirculation of deep-dewatering filtrate to the influent of wastewater treatment plant was feasible.

A Novel Approach to Reduce the Environmental Footprint of Maritime Shipping

Maritime shipping is a strategic sector with a strong international vocation and management. The need to define regulations valid for many different countries without generating disparities of treatment slowed down the formulation of environmental regulations, especially for atmospheric emissions. In particular, regulations pertaining to the reduction of sulphur compounds allowed two distinct approaches: the use of low-sulphur fuels or exhaust gas cleaning systems, the so-called Scrubbers. The actual implementation of these solutions presents specific concerns either related to the toxicity of atmospheric by-products and to the fuel cost or to the generation of polluting washwaters that may need treatment before discharge. In this paper we analyzed the potential environmental benefit deriving from the use of a distillate fuel, not compliant with current IMO Sulphur Regulations, together with a Scrubber. The pilot-scale experimental results indicated that a limited amount of water and/or scrubber volume is needed to reduce sulphur emissions below regulations on maritime shipping, especially with the addition of NaOH reaching a water-saving between 25%-33% compared to the use of pure seawater. Experiments indicated that scrubber washwater PAHs emissions are within the available water quality standards indicated by EU and USA guidelines. A bottom-up analysis on heavy metals concentration shed light on the prominent role of metal-parts corrosion on the washwater emissions. Taking into account for corrosion phenomena, the actual heavy metals concentration in the washwater deriving from scrubbing was normally below the water quality standards.

Life cycle assessment of the anaerobic co-digestion of used disposable nappies and expired food products

A novel used disposable nappies treatment method through their anaerobic co-digestion with expired food products developed by the authors is assessed for its environmental impact through Life Cycle Assessment, with a functional unit 1000 kg of mixed waste. The analysis was based on pilot-scale experimental results, laboratory analysis of streams composition, and mass and energy balance of the process, considering the process products (energy, compost, irrigation water, recyclable plastics and adsorbent material). The results are compared to four established baseline scenarios for the treatment of the wastes examined based on incineration and landfilling. The results indicate that the proposed process has a positive environmental impact, averting the emission of 48.1 kg of CO2 eq. and the consumption of 847 MJ of resources per FU, compared to the production of 34.4 kg of CO2 eq. and the consumption of 98.7 MJ of resources per FU from landfilling (net benefit of 82.5 kg of CO2 eq. and 946 MJ per FU). Moreover, the process caused 7 10−7 DALY (disability-adjusted life years) and 0.06 PDF m2 y (potentially disappeared fraction of species) less damage in the human health and ecosystem quality categories compared to landfilling. The process had a single score of −14.7 mPt (normalized damage per functional unit), when direct land application of the digestate was examined instead of compost production and irrigation of the liquid fraction of the digestate (−4.5 mPt).

Experimental study and demonstration of pilot-scale, dry feed, oxy-coal combustion under pressure

Pressurized oxy-combustion is a promising technology for low-carbon, fossil fuel utilization. It has the potential of improved efficiency and economics compared with conventional atmospheric pressure oxy-combustion. Washington University in St. Louis has proposed a new pressurized oxy-combustion process, namely Staged Pressurized Oxy-Combustion, which has the potential to improve further the plant efficiency, operational flexibility, and economics. This process burns pulverized coal in a pressurized, oxy-combustion environment, which has not been demonstrated in a pilot-scale system before. To address this gap, a 100 kWth pressurized oxy-combustion facility was designed and constructed. This facility has a unique burner and furnace design featuring a co-axial, low-mixing flow field, which is drastically different from conventional coal-fired boiler designs where strong mixing is sought by introducing swirl or recirculating flows. This work aims to present the first pilot-scale experimental results of a dry-feed, pressurized oxy-combustion system. The tests focused on exploring flame stability and shape, char burnout, and fine particulate matter formation. Testing results suggest that the burner has excellent flame stability. The flame shape is consistent with the design philosophy and agrees with large eddy simulations. Importantly, complete char combustion can be achieved with an oxygen mole fraction in the flue gas of only 0.8%, as opposed to a required value of ~3% for conventional atmospheric pressure air-fired or oxyfuel combustion, which reduces the costs of both oxygen generation upstream and oxygen removal downstream. The testing results show promise for dry-feed, pressurized oxy-combustion, and the new burner and furnace design.

Purification and concentration of antioxidative dipeptides obtained from chicken extract and their application as functional food

In Japan, about 150,000 tons of egg-laying hens are discarded annually because quality of their meet is low. In order to add further value to carcasses of the spent egg-laying hens and utilize them, an efficient purification and concentration process for functional dipeptides in chicken extract obtained from these carcasses was developed in this study by combining ion-exchange chromatography and nanofiltration (NF) treatment. The functional dipeptides, Anserine and Carnosine, consisting of β-alanine and L-histidine (ACmix), showed a basic property and could be adsorbed directly onto a cation exchange resin. The ACmix were completely separated from other chicken extract elements when the chicken extract was passed through the column packed with cation exchanger and the dipeptides were eluted from the column by using diluted alkaline solution. Major contaminated substances in the ACmix after ion-exchange chromatography were Na+, K+ and creatinine. A NF membrane could remove these contaminants and concentrate ACmix without any heat treatment. Based on the results of pilot scale experiments, a mathematical model which could express efficiency of a NF process was newly proposed. By using the mathematical model, an industrial scale NF process which could process 3.6 tons of carcasses in a day were designed, where minimum purify and yield of ACmix in the final product were set at 90% and 95%, respectively. The ACmix had an antioxidant activity specifically to hypochlorite radicals and markedly reduced an oxidative stress in normal human volunteers in combination with vitamin C and ferulic acid.

Three-phase simulation of the hydraulic characteristics of an optimized Chinese dome digester using COMSOL Multiphysics

Domestic (household) biogas plants constitute a growing sub-sector of the anaerobic digestion industry worldwide but have received low interest for improvements. The Chinese dome digester (CDD 1), a major type of domestic biogas plants, is a naturally mixed, unheated and low technology reactor mainly used in rural and pre-urban areas for cooking using animal manure. In this study, a multiphase Computational Fluid Dynamics (CFD) model was applied to evaluate an optimized CDD design and outcomes were compared with results of pilot scale experiments. The optimized digester (CDD2) under goes self-agitating cycles created by the pressure variation from the produced biogas with the aid of a baffle at the top of the reactor, whereas the blank (CDD 1) does not self-agitate. The optimized digester has two pressure zones to improve mixing viz. the self-agitation cycles. The optimized digester is characterized by more, stable and improved hydraulic characteristics and mixing.

Real-time monitoring of the moisture content of filter cakes in vacuum filters by a novel soft sensor

The moisture content of filter cakes is probably the most important characteristic that should be kept at a desired level in industrial cake filtration applications to maintain consistent product quality and minimize energy consumption. Most of the currently applied methods for contactless real-time monitoring of the moisture content are based for example on x-ray or microwave techniques, and therefore, the equipment for the purpose is highly specialized. This paper introduces a novel soft sensor for filter cake moisture estimation that uses machine learning algorithms and data collected with basic process instrumentation. The method is primarily based on the cooling effect observed in the cake and air, caused by evaporation of liquid from the cake during the dewatering period, and it can be supported by other process data. The specific energy consumption of vacuum filtration and the subsequent thermal drying to zero moisture is also analyzed. The results of pilot-scale experiments with calcite slurry and a horizontal belt vacuum filter show that in order to minimize the specific energy consumption of vacuum filtration, it is crucial to find the right combination of slurry concentration, vacuum level, and mass of filter cake per unit area. The proposed method for estimating the filter cake moisture content is especially suitable for real-time monitoring and control, enabling also considerable reduction in the energy consumption of the overall process. When applying the proposed soft sensor method in a pilot-scale process, the mean absolute error of the estimated moisture content of the filter cake is ∼0.4 percentage points when the temperature of air at the vacuum pump inlet and the vacuum pump air flow rate are included in the input variables.

Novel design concept for a commercial-scale plant for supercritical water oxidation of industrial and sewage sludge

Supercritical water oxidation (SCWO) is a promising chemical technology for organic waste water and sludge treatment. Our team has successfully constructed the first pilot-scale SCWO plant in China, and the design concept for our first commercial-scale plant is reported in this paper. The challenges that hinder the commercial development of SCWO are introduced, including corrosion, plugging, high investment and operating costs. Some important lab-scale and pilot-scale experimental results are shown, and some key design parameters for the commercial plant are proposed. The technological process, specialized equipment design and new system flowsheet are described objectively. Moreover, an estimate of the equipment investment and operating costs of this commercial plant is carried out, and a comparison is made with other commercial sludge SCWO plants. This information is valuable for guiding how to best design commercial SCWO plants for the treatment of sludge and other feedstocks including solid particles.

Effects of temperature on the performance of anaerobic co-digestion of vegetable waste and swine manure.

The amount of vegetable wastes (VW) obtained from vegetable supply chain increased rapidly in recent years in China, which has posed environmental pollution problems. In view of the high moisture and organic content of VW, anaerobic digestion (AD) has shown to be an alternative with multi-environmental benefits such as waste disposal and renewable energy production. In this research, the anaerobic co-digestion of VW and swine manure (SM) in a 10 L fed-batch anaerobic digester was investigated, and the effects of temperature at psychrophilic (20°C), mesophilic (32°C and 37°C) and thermophilic (55°C) conditions on biogas production characteristics were studied with the aim of finding the better temperature for the enhanced performance of co-digestion. The results indicated that the operation performance of the anaerobic digester were maintained stability with no accumulation of volatile fatty acids (VFA) at mesophilic and thermophilic condition, as indicated by the low VFA/alkalinity ratio, which was lower than 0.10. The results of anaerobic co-digestion also showed that the value of pH, ammonia nitrogen (NH4+-N) and VFA ranked in normal range. The optimal temperature for co-digestion of VW with SM was mesophilic digestion at 32°C. Under this condition, the biogas and methane production yields reached 463.16 L/kg VS and 256.24 L CH4/kg VS, respectively. The average methane content in biogas at 32°C was the highest and reached 55.33%. Anaerobic digestion at 37°C and 55°C provided slightly lower methane yields of 93.75 L CH4/kg VS and 143.16 L CH4/kg VS, respectively. The lowest methane yield of 22.17 L CH4/kg VS was obtained at 20°C, with 22.88% of methane composition in biogas. The pilot-scale experimental results in 3 m3 household biogas digester showed that the cumulative biogas production was 70.52 m3 during the 42 d fermentation period. The average daily biogas production was 1.680 m3 and the average content of CH4 was 58.2%. The experimental results showed that the co-digestion with VW and SM at 32°C in a household biogas system could improve the stability of anaerobic process and achieve a higher biogas yield, which can satisfy farmers’ domestic biogas demand. Keywords: vegetable wastes, swine manure, anaerobic co-digestion, temperature, household biogas digester DOI: 10.25165/j.ijabe.20181101.3706 Citation: Ren H W, Mei Z L, Fan W G, Wang Y J, Liu F F, Luo T, et al. Effects of temperature on the performance of anaerobic co-digestion of vegetable waste and swine manure. Int J Agric & Biol Eng, 2018; 11(1): 218–225.

Effects of temperature on the performance of anaerobic co-digestion of vegetable waste and swine manure

The amount of vegetable wastes (VW) obtained from vegetable supply chain increased rapidly in recent years in China, which has posed environmental pollution problems. In view of the high moisture and organic content of VW, anaerobic digestion (AD) has shown to be an alternative with multi-environmental benefits such as waste disposal and renewable energy production. In this research, the anaerobic co-digestion of VW and swine manure (SM) in a 10 L fed-batch anaerobic digester was investigated, and the effects of temperature at psychrophilic (20°C), mesophilic (32°C and 37°C) and thermophilic (55°C) conditions on biogas production characteristics were studied with the aim of finding the better temperature for the enhanced performance of co-digestion. The results indicated that the operation performance of the anaerobic digester were maintained stability with no accumulation of volatile fatty acids (VFA) at mesophilic and thermophilic condition, as indicated by the low VFA/alkalinity ratio, which was lower than 0.10. The results of anaerobic co-digestion also showed that the value of pH, ammonia nitrogen (NH4+-N) and VFA ranked in normal range. The optimal temperature for co-digestion of VW with SM was mesophilic digestion at 32°C. Under this condition, the biogas and methane production yields reached 463.16 L/kg VS and 256.24 L CH4/kg VS, respectively. The average methane content in biogas at 32°C was the highest and reached 55.33%. Anaerobic digestion at 37°C and 55°C provided slightly lower methane yields of 93.75 L CH4/kg VS and 143.16 L CH4/kg VS, respectively. The lowest methane yield of 22.17 L CH4/kg VS was obtained at 20°C, with 22.88% of methane composition in biogas. The pilot-scale experimental results in 3 m3 household biogas digester showed that the cumulative biogas production was 70.52 m3 during the 42 d fermentation period. The average daily biogas production was 1.680 m3 and the average content of CH4 was 58.2%. The experimental results showed that the co-digestion with VW and SM at 32°C in a household biogas system could improve the stability of anaerobic process and achieve a higher biogas yield, which can satisfy farmers’ domestic biogas demand. Keywords: vegetable wastes, swine manure, anaerobic co-digestion, temperature, household biogas digester DOI: 10.25165/j.ijabe.20181101.3706 Citation: Ren H W, Mei Z L, Fan W G, Wang Y J, Liu F F, Luo T, et al. Effects of temperature on the performance of anaerobic co-digestion of vegetable waste and swine manure. Int J Agric & Biol Eng, 2018; 11(1): 218–225.

Operational Performance and Microbial Community Structure in a Completely Mixed Aeration System

A completely mixed aeration system was introduced in domestic sewage treatment, and the simultaneous nitrification and denitrification process and microbial community structure were further investigated. The pilot-scale experimental results showed that the operation of the system was stable and the average chemical oxygen demand (COD), NH4+-N and total nitrogen (TN) removal were 93.2%, 96.9% and 75.2%, respectively. The effluent COD, NH4+-N and TN were better than the standard of level A stipulated by Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) in the absence of external carbon source. The sludge derived from the system showed a significant denitrification capacity and the denitrification rate was 2.86 times higher than that in the wastewater treatment plant. In addition, the existence of aerobic denitrifying bacteria in the system was confirmed by the PCR amplification of genes encoding perplasmic nitrate reductases. The high-throughput sequencing results revealed that Zoogloea, Thauera and Dechloromonas were dominant in the completely mixed aeration system.

Taking a reflexive TRL3-4 approach to sustainable use of sunflower meal for the transition from a mono-process pathway to a cascade biorefinery in the context of Circular Bioeconomy

The screening of sustainable agro-industrial biorefinery pathways for the production of bio-based products and energy is a complex challenge and needs investigation. Critical tools for predicting the commercialization feasibility of biorefining pathway includes laboratory and pilot-scale experimental results, processes modeling, technoeconomic and market analysis. The objective of the present study was the potential pathways experimental proof of concept of the sunflower meal (SFM), by-product in the sunflower oil production process, at TRL3-4 level, in an effort to assist the bio-based industries in evaluating the profitability of different possible production routes and product portfolios. Taking a reflexive approach, various processes and products were investigated, adding insights in the technical feasibility of conversion towards multi-product pathways at lab scale. Many sets of experiments were conducted in two laboratories, investigating SFM biorefining using physical, biological and thermochemical processes (fractionation, fermentation, enzymatic hydrolysis and pyrolysis) for the production of various added-value products, biochar and energy carriers. Product yields, mass balances, Effective Mass Yield (EMY) and Feature Complexity (FC) were estimated for each pathway. The study demonstrated that SFM cascade refining concept is feasible leading to the production of antioxidants, protein isolate, biochar, bioenergy carriers (pyro-oil and pyro-gas) and also poly(3-hydroxybutyrate) and microbial oil with a Feature Complexity (FC): 6-7. The studied pathways were based on the principle of optimised resource utilisation. Pyrolytic chars showed suitable for soil amendment, thus, closing the loop in agriculture (from land-to-land). The study demonstrated at TRL3-4, alternative pathways for sifting from a mono-to-multiple process and product agricultural industry (Grey biotechnology), in the context of Circular Bioeconomy and provided experimental protocols.

Experimental investigation and prediction of oxygen transfer in vortex flow regulators

We are the first to report pilot-scale experimental results on aeration efficiency of standard and newly developed cylindrical flow regulators (CVRs), conducted over a wide range of operational conditions, geometries and regulator types. In this work, two new (patented) constructions (CVR-2 and CVR-U) are introduced; they are aimed at enhancing reaeration capacity. They are compared with a standard cylindrical vortex regulator (CVR) optimised for flow control and throttling only. The aim of the study was also to understand the mechanisms that govern the aeration of vortex regulators. We have selected and studied the influence of key parameters on oxygen mass transfer in the vortex flow regulators in head-to-head comparisons. We prove that the reaeration capacity of CVRs is not linearly proportional to the number of active outlets, as multiple competing phenomena are responsible for the final aeration efficacy. We show that by changing the arrangement of the active outlets, it is possible to increase the aeration efficiency up to 20%. In the practical situations, this feature is beneficial in enhancing the aeration capacity of flow regulators and it does not degrade throttling properties. In order to allow practical application, the empirical formulas were developed to predict oxygen transfer efficiency. The investigations reported in this paper are expected to be transferable to other vortex regulators that exhibit similar flow hydrodynamics, especially those with a conical vortex chamber.

Performance and energy aspects of single and two phase thermophilic anaerobic digestion of waste activated sludge

The study reported in this paper considered the results of pilot-scale experiments on single and 2-phase anaerobic digestion of waste activated sludge at high rate. Both single and 2-phase digesters were conducted at the same conditions of organic loading and retention time. The 2-phase anaerobic system showed clear increases in terms of organic matter removal and biogas production compared to the single stage system. Particularly, the volatile solids removal rose from 34% in the single stage system to 38% in the 2-phase system. Hence, the global specific biogas production increased 32%, moving from 0.21 to 0.31 m3/kgTVS·d respectively for the single and 2-phase systems. The 2-phase system produced 15% more energy than the single stage system. Furthermore, the heat produced in a CHP unit satisfied all heat requirements insuring more than the complete energetic sustainability of the process. Finally, both single and 2-phase digestates showed to meet requirements established for sludge reuse in agriculture regarding pathogens, metals and organic contaminants. A preliminary economic analysis showed the possibility to pay back the investment for the implementation of a second anaerobic reactor in 3 years because of both the increased biogas production and reduced quantity of excess sludge to be disposed of.

Simulation and analysis of CO2 capture process with aqueous monoethanolamine solution

An improved rate-based model of the typical CO2 capture process by aqueous MonoEthanolAmine (MEA) solution is built within Aspen Plus V8.0 software in this study. The improved model is built on the basis of an example model coming along with Aspen Plus V8.0, and thermodynamic model of ENRTL-RK is adopted. Improvements include the washing section of the absorption column is strictly modelled by a separate column, and the error on mass balance of MEA is greatly reduced. The new model is validated by the recently published pilot-scale experimental results of the absorption of CO2 by MEA solution, in which both absorption and desorption columns are equipped with the structured packing Sulzer Mellapak 250.Y™. It predicts the experimental profiles of the temperature and the concentration of CO2 in the liquid phase with an accuracy of ±4%, and obviously much better than recently reported model with an accuracy of ±8%. Important insights have been obtained on the function of washing sections on the top of both absorber and desorption column, the factors to determine the flowrates of make-up water and recycle water around the washing section of the absorber are first analyzed.

Comprehensive utilization of phosphate in a highly concentrated recirculating cooling water system using secondary-treated municipal wastewater as make-up

A comprehensive utilization process using phosphate was developed for the reuse of high hardness secondary-treated municipal wastewater to a highly concentrated recirculating cooling water system (RCWS). It showed that the soluble phosphate in the wastewater could be directly reused as a corrosion inhibitor to prevent the RCWS from severe corrosion caused by the contaminants in the wastewater. Based on the synergetic corrosion inhibition of PO43- and Zn2+, a chemical program was achieved for recirculating cooling water treatment. It contains 1-hydroxyethylidene-1,1-diphosphonic acid, polyepoxysuccinic acid, zinc sulfate heptahydrate, and a copolymer dispersant of LN-104B. In addition, LN-104B was verified to have excellent inhibition capability to calcium phosphate scale and zinc salts scale in the bench experiments. The pilot-scale experimental results showed that the simulated RCWS operated very well under the condition of high Ca2+ concentration (1,500 mg/L as CaCO3) using the chemical program and automatic pH-controlled technique. The corrosion rate and the adhesion rate of the test tubes are only 0.023 mm/a and 2.32 mcm, respectively, which perfectly meet the requirements of the international standard of ISO 16784-2006. Not only can the process cut down the operating cost of RCWS, but also can reduce the environmental risk caused by excessive emission of phosphate. Moreover, large amounts of fresh water and phosphorus resources are expected to be conserved.