Phosphorus attenuation and mobilization in sand filters treating onsite wastewater.

The effectiveness of phosphorus (P) removal by sand filters is limited during septic tank effluent (STE) treatment. The elevated effluent P concentrations pose threats to drinking water quality and contribute to eutrophication. The concern of P leaching from sand filters is further exacerbated by the increased frequency of flooding and natural precipitation due to climate change. This study aimed to understand P attenuation and leaching dynamics, as well as the removal mechanisms in sand filters treating STE, offering insights into the design and implementation of P removal/recovery modules to onsite wastewater treatment systems. P attenuation and leaching during STE treatment and rainfall were studied in bench-scale columns (new vs. aged sand). At standard STE loading (1.2 gallon d-1 ft-2), 24-32% removal of total phosphorus (TP) was achieved, while increased P removal efficiency (35-53%) was observed at low loading (0.6 gallon d-1 ft-2) with influent containing 10.3-20.0 mg P L-1. Complete breakthroughs were observed in both aged (12-70 days) and new columns (27-73 days) at test hydraulic loadings. The maximum TP attenuation level was 20.6-45.3 mg P kg-1 and 25.3-33.0 mg P kg-1, in aged and new sand columns, respectively. When simulated rain was applied (15-60 mm h-1), 80-97% of the attenuated P leached out and the leaching dynamics were impacted by rainfall duration rather than the intensity. The highest concentrations of TP (15.6-15.9 mg L-1) were leached out from both columns within the first 2-6 h. Orthophosphate was the dominant P species in treated effluent (83-84%) and leachate (69-88%), demonstrating its significance as the major P form in the discharge. In addition, aged sand (>5 years) accumulated higher levels of Mg, Al, Ca, and Fe, thus enhancing the P attenuation level during STE treatment. Collectively, this study underscored the importance of frequent field monitoring for reliable long-term P removal estimates.

Constraining the formation of authigenic carbonates in a seepage-affected cold-water coral mound by lipid biomarkers.

Cold-water coral (CWC) mounds are build-ups comprised of coral-dominated intervals alternating with a mixed carbonate-siliciclastic matrix. At some locations, CWC mounds are influenced by methane seepage, but the impact of methane on CWC mounds is poorly understood. To constrain the potential impact of methane on CWC mound growth, lipid biomarker investigations were combined with mineralogical and petrographic analyses to investigate the anaerobic oxidation of methane (AOM) and authigenic carbonate formation in sediment from a seep-affected CWC mound in the Gulf of Cadiz. The occurrence of AOM was confirmed by characteristic lipids found within a semi-lithified zone (SLZ) consisting of authigenic aragonite, high-magnesium calcite and calcium-excess dolomite. The formation of high-Mg calcite is attributed to AOM, acting as a lithifying agent. Aragonite is only a minor phase. Ca-excess dolomite in the SLZ and upper parts may be formed by organoclastic sulphate reduction, favouring precipitation by increased alkalinity. The AOM biomarkers in the SLZ include isoprenoid-based archaeal membrane lipids, such as abundant glycerol dibiphytanyl glycerol tetraethers (GDGTs) dominated by GDGT-2. The δ13 C values of GDGT-2, measured as ether-cleaved monocyclic biphytanes, are as low as -100‰ versus V-PDB. Further, bacterial dialkyl glycerol diethers with two anteiso-C15 alkyl chains and δ13 C values of -81‰ are interpreted as biomarkers of sulphate-reducing bacteria. The lipid biomarker signatures and mineralogical patterns suggest that anaerobic methane-oxidizing archaea of the ANME-1 group thrived in the subsurface at times of slow and diffusive methane seepage. Petrographic analyses revealed that the SLZ was exhumed at some point (e.g. signs of bioerosion of the semi-lithified sediment), providing a hard substrate for CWC larval settlement. In addition, this work reveals that AOM-induced semi-lithification likely played a role in mound stabilization. Lipid biomarker analysis proves to be a powerful tool to disentangle early diagenetic processes induced by microbial metabolisms.

Calcium-ammonium exchange experiments on clay minerals using a (45)Ca tracer technique in marine pore water.

Understanding cation exchange processes is important for evaluating early diagenetic and synsedimentary processes taking place in marine sediments. To quantify calcium (Ca) exchange and Ca-ammonium exchange in a seawater environment, we performed experiments with a radioactive (45)Ca tracer on clay mineral standards (Fithian illite, montmorillonite and kaolinite) and marine sediments from the North Atlantic Integrated Ocean Drilling Program Site U1306A in artificial seawater (ASW). The results show that equilibrium during the initial attachment of Ca as well as the exchange of Ca by [Formula: see text] is attained in less than 2 min. On average 8-20% of the exchangeable sites of the clay minerals were occupied by Ca in a seawater medium. The conditional selectivity coefficient, describing the [Formula: see text] exchange in ASW is mineral specific and it was determined to be 0.07 for montmorillonite, 0.05 for a natural marine sediment and 0.013 for Fithian illite.

Resistance of Lophelia pertusa to coverage by sediment and petroleum drill cuttings.

In laboratory experiments, the cold-water coral Lophelia pertusa was exposed to settling particles. The effects of reef sediment, petroleum drill cuttings and a mix of both, on the development of anoxia at the coral surface were studied using O2, pH and H2S microsensors and by assessing coral polyp mortality. Due to the branching morphology of L. pertusa and the release of coral mucus, accumulation rates of settling material on coral branches were low. Microsensors detected H2S production in only a few samples, and sulfate reduction rates of natural reef sediment slurries were low (<0.3 nmol S cm(-3) d(-1)). While the exposure to sediment clearly reduced the coral's accessibility to oxygen, L. pertusa tolerated both partial low-oxygen and anoxic conditions without any visible detrimental short-term effect, such as tissue damage or death. However, complete burial of coral branches for >24 h in reef sediment resulted in suffocation.