Stripping and scrubbing of ammonium using common fractionating columns to prove ammonium inhibition during anaerobic digestion

Anaerobic digestion to produce biogas is generally considered as one of the most sustainable technologies for the production of renewable energy. During this microbial process, organically bound nitrogen is released as ammonium that ends up in the digestate and finally may inhibit the process. In this study, it is investigated if ammonium can be removed and recovered out of the liquid fraction of a thermophilic digestate from a potato processor. This is achieved at laboratory scale through an easy and self-designed stripping and scrubbing process using Vigreux and Dufton columns, which are commonly used laboratory fractionating columns. The stripping is performed at pH 8.5 and at 323.15K (50 degrees C), which results in the volatilization of the ammonium present in ammonia. Subsequently, the stripping gas charged with ammonia is put into contact with a sulphuric acid solution, resulting in (NH4)(2)SO4, which can be used as an N-S fertilizer. In addition, the digestion experiments have demonstrated that the biogas yield is 36% higher after removal of the ammonium from the digestate compared to the untreated digestate

Effects of Bioleaching on the Chemical, Mineralogical and Morphological Properties of Natural and Waste-Derived Alkaline Materials

Bioleaching is a potential route for the valorisation of low value natural and waste alkaline materials. It may serve as a pre-treatment stage to mineral carbonation and sorbent synthesis processes by increasing the surface area and altering the mineralogy of the solid material and by generating an alkaline rich (Ca and Mg) aqueous stream. It may also aid the extraction of high value metals from these materials (e.g. Ni), transforming them into valuable ore reserves. The bioleaching potential of several bacteria (Bacillus circulans, Bacillus licheniformis, Bacillus mucilaginosus, Sporosarcina ureae) and fungi (Aspergillus niger, Humicola grisea, Penicillium chrysogenum) towards the alteration of chemical, mineralogical and morphological properties of pure alkaline materials (wollastonite and olivine) and alkaline waste residues (AOD and BOF steel slags, and MSWI boiler fly ash) at natural pH (neutral to basic) was assessed. Bioleaching was conducted using one-step and two-step methodologies. Increased solubilisation of alkaline earth metals and nickel were verified. Alteration in basicity was accompanied by alteration of mineralogy. AOD slag experienced solubilisation-precipitation mechanism, as evidenced by the decline of primary phases (such as dicalcium-silicate, bredigite and periclase) and the augmentation of secondary phases (e.g. merwinite and calcite). Nickel-bearing minerals of olivine (clinochlore, lizardite, nimite and willemseite) significantly diminished in quantity after bioleaching. Altered mineralogy resulted in morphological changes of the solid materials and, in particular, in increased specific surface areas. The bioleaching effect can be attributed to the production of organic acids (principally gluconic acid) and exopolysaccharides (EPS) by the microorganisms. The similarities between fungal and bacterial mediated bioleaching suggest that biogenic substances contribute mostly to its effects, as opposed to bioaccumulation or other direct action of living cells

The inhibitory effect of inorganic carbon on phosphate recovery from upflow anaerobic sludge blanket reactor (UASB) effluent as calcium phosphate

After treatment of the wastewater from the potato processing industry in an upflow anaerobic sludge blanket reactor (UASB) the effluent is rich in phosphate and dissolved inorganic carbon (IC). Increasing the pH of the UASB effluent with NaOH to precipitate phosphate as calcium phosphate leads to contamination with magnesium phosphate. Increasing the pH with Ca(OH)2 had a positive effect on phosphate precipitation, but after increasing the pH with Na2CO3 no precipitate was formed. After prior nitrification of the UASB effluent to remove IC, less NaOH was needed to increase the pH and the ions precipitated in a ratio that agreed with calcium phosphate formation. When the pH of the nitrified effluent was increased with Na2CO3 neither calcium nor phosphate precipitated. This inhibitory effect of IC on phosphate precipitation as calcium phosphate could not be derived from the saturation indexes calculated by the geochemical modelling program PHREEQC.status: publishe

Performance analysis and optimization of autotrophic nitrogen removal in different reactor configurations: a modeling study

In most modern wastewater treatment plants (WWTP) nitrogen, which is generally in the form of ammonium or organic nitrogen, is removed by biological nitrification - denitrification. This process consists of two steps: nitrification, where ammonium is oxidized to nitrate and denitrification, in which the formed nitrate is reduced to nitrogen gas under anoxic conditions by means of COD (Chemical Oxygen Demand) (Metcalf and Eddy 1991). However, there are some serious disadvantages: aeration costs, excessive sludge production and dependence on (external) carbon source. A new process for high loaded nitrogen streams, including partial nitritation and Anammox (ANaerobic AMMonium OXidation), eliminates these disadvantages. Half of the incoming ammonium is transformed to nitrite in the first step (partial nitritation, rate NH4+/NO2- = 1). Next, the formed nitrite and the remaining ammonium is converted into nitrogen gas under anaerobic conditions (Anammox). This process can be applied to treat ammonium-rich wastewater, for instance water from a sludge digester at a WWTP (Mulder et al. 2001; Hellinga et al. 1998). The drawback of the Anammox bacteria is their slow growth rate, which has a negative effect on the start-up time of such reactor, making experimental studies difficult. As a consequence, preventing the wash out of these organisms is in this case very important (Strous et al. 1998; Jetten et al. 1998). The goal of this thesis was testing different reactor configurations in order to analyze the influence of varying parameters on these systems. The three elaborately tested CASR reactors (Conventional Activated Sludge Reactor) are an oxygen limited partial nitritation reactor, an Anammox reactor and a combination of partial nitritation and Anammox in one single reactor. All three were tested under different parameter settings of temperature, pH, biomass retention, nitrogen load, COD and HRT (Hydraulic Retention Time). The software program WEST® (MOSTforWATER) was used to obtain the results of this modeling study

Evaluation and thermodynamic calculation of ureolytic magnesium ammonium phosphate precipitation from UASB effluent at pilot scale

The removal of phosphate as magnesium ammonium phosphate (MAP, struvite) has gained a lot of attention. A novel approach using ureolytic MAP crystallization (pH increase by means of bacterial ureases) has been tested on the anaerobic effluent of a potato processing company in a pilot plant and compared with NuReSys (R) technology (pH increase by means of NaOH). The pilot plant showed a high phosphate removal efficiency of 83 +/- 7%, resulting in a final effluent concentration of 13 +/- 7 mg . L-1 PO4-P. Calculating the evolution of the saturation index (SI) as a function of the remaining concentrations of Mg2+, PO4-P and NH4+ during precipitation in a batch reactor, resulted in a good estimation of the effluent PO4-P concentration of the pilot plant, operating under continuous mode. X-ray diffraction (XRD) analyses confirmed the presence of struvite in the small single crystals observed during experiments. The operational cost for the ureolytic MAP crystallization treating high phosphate concentrations (e.g. 100 mg . L-1 PO4-P) was calculated as 3.9 (sic) kg(-1) P-removed. This work shows that the ureolytic MAP crystallization, in combination with an autotrophic nitrogen removal process, is competitive with the NuReSys (R) technology in terms of operational cost and removal efficiency but further research is necessary to obtain larger crystals

Autotrophic nitrogen removal after ureolytic phosphate precipitation to remove both endogenous and exogenous nitrogen

Anaerobic digestion yields effluents rich in ammonium and phosphate and poor in biodegradable organic carbon, thereby making them less suitable for conventional biological nitrogen and phosphorus removal. In addition, the demand for fertilizers is increasing, energy prices are rising and global phosphate reserves are declining. This requires both changes in wastewater treatment technologies and implementation of new processes. In this contribution a description is given of the combination of a ureolytic phosphate precipitation (UPP) and an autotrophic nitrogen removal (ANR) process on the anaerobic effluent of a potato processing company. The results obtained show that it is possible to recover phosphate as struvite and to remove the nitrogen with the ANR process. The ANR process was performed in either one or two reactors (partial nitritation + Anammox). The one-reactor configuration operated stably when the dissolved oxygen was kept between 0.1 and 0.35 mg L-1. The best results for the two-reactor system were obtained when part of the effluent of the UPP was fully nitrified in a nitritation reactor and mixed in a 3: 5 volumetric ratio with untreated ammonium-containing effluent. A phosphate and nitrogen removal efficiency of respectively 83 +/- 1% and of 86 +/- 7% was observed during this experiment

Simulation and evaluation of the ureolytic magnesium ammonium phosphate precipitation from UASB effluent at pilot scale

status: accepte

The fate of nitrite and nitrate during anaerobic digestion

Anaerobic digestion is widely used to produce renewable energy. However, the main drawback is the limited conversion efficiency of organic matter. Applying an advanced oxidation process as a digestate post-treatment is able to increase this conversion efficiency but will also lead to the oxidation of ammonium to nitrite or nitrate. In this lab-scale study, the fate of the latter in the digester was investigated. Nitrite and nitrate were therefore added in concentrations that could arise from rate-limiting ammonium concentrations (1.25-5 g L-1 N). The study clearly demonstrated that nitrite and nitrate were denitrified during the subsequent digestion process resulting in the formation of nitrogen gas. After a concentration-dependent adaptation period, in which some biogas was produced, the added nitrite was denitrified in amounts proportional to the amounts of electron donor present. This denitrification, however, strongly reduces the possibility that Anammox bacteria can develop. Nitrate was also denitrified in amounts proportional to the amounts of electron donor, but biogas production was not completely blocked in this case. Moreover, high concentrations of nitrite and nitrate inhibited their own denitrification. The methane formed was used as electron donor for the further denitrification of nitrate and nitrite when no other readily available electron donor was present. After addition of either nitrite or nitrate and their denitrification, the biogas production did not recover properly