Using landfill leachate to indicate the chemical and biochemical activities in elevated temperature landfills.

Landfill leachate properties contain important information and can be a unique indicator for the chemical and biochemical activities in landfills. In the recent decade, more landfills are experiencing elevated temperature, causing an imbalance in the decomposition of solid waste and affecting the properties of the landfill leachate. This study analyzes the properties of leachate from two landfills that were experiencing elevated temperature (ETLFs), samples were collected from both elevated temperature impacted and non-impacted areas in each landfill. The accumulation of volatile fatty acids (VFA) in leachates from elevated temperature impacted areas of both landfill sites revealed that methanogenesis was inhibited by the elevated temperature, which was further confirmed by the more acidic pH, higher H/C elemental ratio, and lower degree of aromaticity of the elevated temperature impacted leachates. Also, carbohydrates depletion indicated possible enhancement of hydrolysis and acidogenesis by elevated temperature, which was supported by compositional comparison of isolated acidic species by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS) at 21 T derived from both elevated temperature impacted and non-impacted areas in the same landfill site. Furthermore, leachate organics fractionation showed that leachates not impacted by elevated temperature contain less hydrophilic fraction and more humic fraction than elevated temperature-impacted leachates for both ETLFs.

Adsorption of recalcitrant phosphorus compounds using the phosphate-selective binding-protein PstS.

Currently available wastewater phosphorus (P) treatment technologies target removal of reactive forms of P. Selective adsorption of more recalcitrant soluble non-reactive phosphorus (sNRP) can improve P removal and recovery. A phosphate-selective phosphate-binding protein (PBP), PstS, was immobilized onto NHS-activated beads to assess the ability of this novel bioadsorbent to remove (adsorb) and subsequently recover (desorb) a range of sNRP compounds. Four sNRP compounds representative of wastewater sNRP were selected for use in this study: phytic acid (PA), sodium triphosphate (TrP), beta-glycerol phosphate (BGP), and sodium hexametaphosphate (HMP). Using PBP, adsorption of all sNRP compounds was thermodynamically favorable. The PBP had nearly equivalent binding affinity for PA compared to PBP's typical target, orthophosphate, although it had less affinity for the other sNRP compounds. Adsorption followed pseudo-second order reaction kinetics, with 95% of maximum adsorption occurring within 4 min. This was substantially faster sNRP adsorption compared to other adsorbents in the literature. Adsorption was modeled using the Langmuir isotherm, reflecting that one phosphate molecule attached to one PBP binding site. Notably, this selective 1:1 attachment resulted in higher total P removal for sNRP molecules with high P content. The binding site lost activity with increasing pH, and as such, highest desorption was achieved at pH 12, making the system amenable to sNRP removal as well as controlled recovery.

Meta-analysis of the prevalence of dissolved organic nitrogen (DON) in water and wastewater and review of DON removal and recovery strategies.

Most wastewater removal and recovery processes primarily target dissolved inorganic nitrogen (DIN) species, leaving the untreated non-reactive dissolved organic nitrogen (DON) in the effluent. This DON fraction can account for a substantial part of the total nitrogen (N) load. We analyzed large datasets of N species and concentrations (with a focus on quantifying the fraction of DON) in surface water, ground water, and wastewater effluent across the United States. We then reviewed strategies to remove and recover DON based on results of a range of treatment technologies reported in the literature, including laboratory-scale up to full-scale operation in wastewater treatment plants. Our meta-analysis showed that DON concentrations are greatest in wastewater effluent followed by surface water and groundwater. The concentration of DON in wastewater effluent varied from 0.01 to 10.9 mg N/L (number of data points, n = 163), where the range in surface water was 0.002 to 14.3 mg N/L (n = 11,803). Organic N accounted for the majority of total N in 12.3% of wastewater effluent samples and 49.1% of surface waters. Our literature review showed that currently available wastewater treatment processes do not efficiently target DON removal nor recovery of the DON as a valuable product. One potential DON removal and recovery strategy is transforming DON into DIN, which is generally more easily removed and recovered. Transformation strategies reported in the literature include ozonation, UV/H2O2, and electrooxidation. However, as advanced oxidation processes are often energy- and cost-intensive, further research is needed to improve DON removal and recovery.

Electro-oxidation to convert dissolved organic nitrogen and soluble non-reactive phosphorus to more readily removable and recoverable forms.

Conventional wastewater treatment processes cannot effectively remove dissolved organic nitrogen (DON) and soluble non-reactive phosphorus (sNRP), which can pose regulatory compliance challenges for total nitrogen and total phosphorus discharges. Moreover, DON and sNRP are not easily recoverable for beneficial reuse as part of the waste to resource paradigm. Conversion of DON and sNRP to more readily removable dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (sRP), respectively, will help meet stringent nutrient limits and facilitate nutrient recovery. In this study, electro-oxidation (EO) was evaluated for conversion of four DON compounds to DIN and five sNRP compounds to sRP. EO was more efficient and provided higher extents of conversion of the recalcitrant nutrient fractions compared to a more traditional advanced oxidation process, UV/H2O2. Direct electron transfer was likely the dominant oxidation mechanism for EO-based DON and sNRP conversion, with DON being more recalcitrant. Among the DON compounds tested, greater availability of primary amine (C-N bonds) yielded greater conversion compared to compounds with fewer primary amine or those with secondary amine (C-N-C bond). Among the sNRP compounds tested, those with P-O-C bonds (organic sNRP) converted more readily than those with P-O-P bonds (inorganic sNRP), presumably because cleavage of the latter bond requires greater energy. Using 30 min of EO treatment, the highest DON and sNRP compound conversion was 11.7 ± 0.09% for urea and 31.1 ± 0.75% for beta-glycerol phosphate. A similar extent of EO-based conversion of DON (6.41 ± 1.5%) and sNRP (32.7 ± 3.3%) was observed in real wastewater.

Conversion of soluble recalcitrant phosphorus to recoverable orthophosphate form using UV/H2O2.

Soluble non-reactive phosphorus (sNRP), such as inorganic polyphosphates and organic P, is not effectively removed by conventional physicochemical processes. This can impede water resource reclamation facilities' ability to meet stringent total P regulations. This study investigated a UV/H2O2 advanced oxidation process (AOP) for converting sNRP to the more readily removable/recoverable soluble reactive P (sRP), or orthophosphate, form. Synthetic water spiked with four sNRP compounds (beta-glycerol phosphate, phytic acid, triphosphate, and hexa-meta phosphate) at varying H2O2 concentration, UV fluence, pH, and temperature was initially tested. These compounds represent simple, complex, organic, and inorganic forms of sNRP potentially found in wastewater. The efficiency of sNRP to sRP conversion depended on whether the sNRP compound was organic or inorganic and the complexity of its chemical structure. Using 1 mM H2O2 and 0.43 J/cm2 (pH 7.5, 22 °C), conversion of the simple organic beta-glycerol phosphate to sRP was 38.1 ± 2.9%, which significantly exceeded the conversion of the other sNRP compounds. Although conversion was achieved, the electrical energy per order (EEO) was very high at 5.2 × 103 ± 5.2 × 102 kWh/m3. Actual municipal wastewater secondary effluent, with sNRP accounting for 15% of total P, was also treated using UV/H2O2. No wastewater sNRP to sRP conversion was observed, ostensibly due to interference from wastewater constituents. Wastewater utilities that have difficulty meeting stringent P levels might be able to target simple organic sNRP compounds, though alternative processes beyond UV/H2O2 need to be explored to overcome interference from wastewater constituents and target more complex organic and inorganic sNRP compounds.