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

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

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

Electrodialysis on RO concentrate to improve water recovery in wastewater reclamation

Over-consumption of groundwater in coastal areas causes seawater intrusion and soil salinization, which is a threat to residents, to agricultural activity and to the ecological system. In this study, a more sustainable approach is investigated based on groundwater recharge of the unconfined aquifer in the dune water catchment area in the western part of the Flemish coast. Ultrafiltration (UF) followed by reverse osmosis (RO) is currently applied to treat the secondary effluent from a wastewater treatment plant (WWFP) for infiltration (groundwater recharge). This paper investigates the feasibility of electrodialysis (ED) on the RO concentrate to reduce the volume of salty water discharge and to improve the overall water recovery to produce infiltration water for groundwater recharge. In the pilot system, the decarbonation process was used to reduce scaling potential of the feed or the concentrate stream of the ED. Based on various experiments in batch and in feed-and-bleed mode, ion transport mechanisms were studied to monitor the effluent water compositions. Meanwhile, a factor named critical scaling concentration (CSC) was established to predict the potential occurrence of scaling. Ozonation was used to improve the biodegradability of the ED effluent hence to reduce the potential of organic compounds accumulation in the recirculation system. Thus, ED was found to be a good option to treat RO concentrates

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