Nitrogen removal from sewage and septage in constructed wetland mesocosms using sand media amended with biochar

Abstract

Biochar has been identified as a media amendment to improve nutrient removal from wastewater, and N retention and plant growth in agroforestry. It therefore has the potential for treating domestic wastewater. The aim of this research was to compare nitrogen removal and plant growth in pure sand and sand amended with biochar, in wetland mesocosms (240 L) receiving sewage. There were seven media treatments based on the proportions of biochar in the sand media (100% sand, sand and coir peat, 5, 10, 15, 20, 25% biochar). The plant species were Paperback tree (Melaleuca quinquenervia) and Lemongrass (Cymbopogon citratus). The mesocosms were continuously loaded for 8 months with secondary clarified wastewater (SCW) (16 L/day). Septage was then intermittently loaded (20 L/2 days) for a further 8 months. Inflow and outflow samples were monitored for TN, NH 4-N, and NO x-N. All treatments showed good nitrogen removal efficiency. Average removal efficiencies of TN, NO x-N and NH 4-N in the mesocosms loaded with SCW ranged from 71 to 87%, 81 to 93% and 65 to 79%, for 100% Sand to 25% Biochar respectively. For septage, the removal efficiencies ranged from 63 to 81%, 69 to 87% and 66 to 81%, for 100% Sand to 25% Biochar respectively. Significant differences of nitrogen outflow concentrations were observed between pure sand and sand amended with biochar. Physical chemical properties of the biochar would have facilitated microbial processes and adsorption. Strong positive correlations were observed between biochar content in the media and nitrogen removal rates. The increased nitrogen removal may be attributed to higher mineralisation of organic nitrogen and NH 4-N, especially in the case of septage where strong correlation was observed between BOD 5 and TN removal. Total N biomass in the plants harvested after 21 months ranged from 13.4-14.0 g N. The addition of biochar did not increase plant N biomass in either species.

Biochar-augmented biofilters to improve pollutant removal from stormwater – can they improve receiving water quality?

“…99 The effect of biochar addition on hydraulic conductivity of biofilter media will depend on the differences in particle size of the biochar and the sand 55,97 and may also depend on the biochar application rate. Addition of biochar to sand media reduced the hydraulic conductivity at higher biochar application rates (>15%), 100 and a ten-fold decrease in hydraulic conductivity compared to sand-only was observed by Ray et al 54 when mixing sand (0.6-0.85 mm) with finer biochar particles (0.1-0.3 mm). On the contrary, biochar application rates of 0.5-2% only led to minimal decreases in hydraulic conductivity of a sandy loam soil.…”

A Review of Nitrogen Removal for Urban Stormwater Runoff in Bioretention System

“…Nitrogen influent concentration is one of the factors that affects nitrogen removal processes. Previous studies have shown that the uptake rate of nitrogen was influenced by the inflow concentration; the removal efficiency was more satisfied with the low nitrogen concentration than the high concentration [72,73]. S. Wang [67] observed that the removal efficiency of NO 3 − was low (20.5%) for an influent concentration ranging from 6.15 to 9.61 mg/L.…”

“…The uptake rate usually depends on the plant type and plant growth rate. In fact, good plant growth with higher biomass will result in a better plant uptake and nitrogen removal [72][73][74][75][76], however, rapid plant growth rate also contributes to TN removal [77]. A study by Milandri et al [78] found that the rapid growth rate of the turf grasses, Pennisetum and Stenotaphrum, was effective in NH 3 (97%) and NO 3 − removal (>80%).…”

Investigating the influence of iron–carbon microelectrolysis on the performance and microbial community of constructed wetlands

“…Constructed wetlands (CWs), as an efficient eco‐technology, have been applied extensively in wastewater treatment because of the advantages of their low cost and simple operation and maintenance (de Rozari et al 2018; Nivala et al 2018). Therefore, with the increase in the world population, urbanization, industrialization and the depletion of water resources, CWs have attracted the attention of most countries around the world (Lu et al 2016).…”