Autotrophic denitrification of synthetic nitrate-contaminated groundwater in up-flow fixed-bed bioreactor by pumice as porous media

Abstract

Background: Background: Increasing nitrate concentrations in groundwater resources is considered a common environmental and public health problem worldwide. In this research, an autotrophic up-flow bioreactor with pumice as media was used to study the effects of the sulfur-to-nitrogen (S/N) ratio and empty bed contact time (EBCT) on nitrate removal efficiency and byproducts. Methods: Experiments were carried out in a 3.47 L up-flow, fixed-bed reactor with 3 sampling ports. To evaluate the overall impact of S/N ratio and EBCT on the performance of the bioreactor, several phases with different S/N ratios and EBCTs were applied. Results: At a constant S/N ratio of 3.85 g/g, as EBCT decreased from 24 hours to 2 hours, the nitrate removal efficiency decreased from 98% to 64%. On the other hand, at the desired EBCT of 4 hr, as S/N ratio decreased from 3.85 to 1.51 g/g, nitrate removal efficiency was reduced from 85% to 32%. Changing the EBCT and S/N ratio also affected the effluent nitrite and sulfate concentrations as byproducts. At the S/N ratio of 3.85 g/g and EBCT of 24 hours, effluent nitrite and sulfate concentrations were 0.1 mg NO 2-N/L and 463 mg SO 4 2-/L, respectively. Decreasing the S/N ratio to 1.51 g/g and the EBCT to 4 hours caused drastic changes in effluent nitrite and sulfate concentrations. Conclusion: The results indicated that the autotrophic denitrification with thiosulfate as electron donor and pumice as media was feasible and applicable for nitrate contaminated groundwater.

Healthcare waste management current status and potential challenges in Ethiopia: a systematic review

“…General and infectious wastes were mixed together [9]. Plastic buckets were used to store the HCW temporarily [17, 27]. Disinfection of waste storage and/or transporting utilities was uncommon [6, 17].…”

“…Low combustion incinerator was used to treat all the HCW types [2, 8, 9, 12, 14, 21, 46]. In other cases, studies indicated the use of incineration and open burning methods to treat hazardous and general wastes, respectively [5, 6, 8, 14, 17, 20, 27]. With respect to disposal of the treated waste by-products, some studies used burial pit [2, 6] while other studies disposed of in an unsanitary way simply by open dumping [8, 12, 27].…”

“…If these facilities are not available, the HCW can be stored in other secured locations [31, 53]. However, studies indicated hazardous waste storage practices using the primary waste segregation containers stationed around the corridors [27, 44]. This unacceptable waste storage practice could probably due to the lack of sufficient and isolated waste storage spaces away from direct public access.…”

“…However, incinerators are often operated under sub-optimal conditions mostly with untrained personnel [4]. Thus, due to inadequate incineration harmful substances can be released into the environment [27]. Regarding disposal of the HCW, incinerator ash is commonly disposed of in burial pit or open dumping.…”

“…Healthcare waste is categorized as general and hazardous waste types [25–27]. General waste is the largest portion [26] which is originated from food preparation, administrative and housekeeping activities.…”