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| Home > Publications database > Systematic case-study: Nutrient cycling from wastewater to crop via Algal Turf Scrubber (ATS) |
| Home > Publications database > Systematic case-study: Nutrient cycling from wastewater to crop via Algal Turf Scrubber (ATS) |
| Talk (non-conference) (Invited) | FZJ-2023-00605 |
;
2022
Please use a persistent id in citations: http://hdl.handle.net/2128/33597
Abstract: Often, small-scale agriculture and industries in remote areas lack the access to cost-effective wastewater (WW) treatment. One techno-economical solution could be WW treatment by algal biofilm in Algal Turf Scrubbers (ATS). Yet, systematic studies, to the efficiency of ATS biofilms in nutrient-recovery from WWs and -release to crops, are limited. Here we present the findings of a case study to 4 pilot-scale ATS operated with 4 WW-types under field conditions for 12 months. We will show results to nutrient transfers, biomass yields, and WW remediation. Further, we will evaluate bioavailability and valorisation of ATS biofilm as slow-release fertiliser or soil improver.INTRODUCTIONIn 2014, the EU declared phosphorous (P) as an essential resource with significant risk to supply, due to its indispensable role as nutrient and its finite deposits in politically instable regions. Yet, excessive application and limited remediation practices caused a chronic loss of phosphorus into the environment. Together with other nutrients, this led to increasing eutrophication of natural water bodies, deterioration of soils, greenhouse gas emissions and public health risks. The recovery of P and closing of nutrient cycles has become vital. And the integration of wastewater remediation and its products in a circular bioeconomy can promote new economically viable technologies. Nutrient cycling by micro- and macroalgae has been successfully demonstrated and could be an environmentally and economically sustainable technology (Siebers, 2019; Solovchenko, 2016; Zou, 2021). The algae are grown in nutrient-rich wastewater, harvested, and processed to feed, fertiliser, or feedstock for further extractions, while the water is cleaned and oxidised. Algal biofilm systems, such as the Algal Turf Scrubbers, can be more cost effective than suspended cultures, due to higher biomass density and easier harvest. Here, we present the first results of a systematic study to the techno-economic challenges and the WW remediation capacity of ATS under field conditions. Materials & MethodsFour identical pilot-scale Algal Turf Scrubber (ATS) were set up (8 m²) with tipping bucket (30 L), medium tank (1 m³), pump (30 L min-1) and IoT sensors (aquatic, environmental). The ATS were operated at a farm and a WWTP with municipal WW, biogas-effluent, pig and cattle manure, respectively. The ATS with mWW was operated in constant mode. The ATS with biogas-effluent, pig and cattle manure received weekly fresh WW (1 m³). All ATS were inoculated with a pre-existing biofilm. ATS biofilms were harvested and analysed weekly (Jul-Oct) or biweekly (Nov-Apr), respectively. Initial characterisation of the 4 WWs was done by a certified external lab. Total phosphorous (TP) and total nitrogen (TN) concentrations were measured at start (d0) and end (d7) of each batch, respectively. Wet and dry weight (DW), ash-, N-, and P-content, and elemental composition of the biofilm were determined at harvest (d7). Population assembly and shifts were monitored microscopically and documented throughout the year. Selected biofilms were analysed for nutrient composition, heavy metals, Chrome (VI), Perfluorate Tenside (PFT), Salmonella sp., E. coli, Enterobacteria, and antibiotics. ResultsThe installation and inoculation of the four ATS-systems were completed in spring 2021. The inoculum derived from an established ATS and was supplemented with a local sample of algal biofilm from the WWTP. Microscopic observation revealed a mesocosm-like assembly of bacteria, pro- and eukaryotic algae, fungi, and protozoa in an extracellular polymeric substance (EPS), Fig. 1. After six weeks, the biofilms covered the complete substrate (8 m²) and pre-cultivation with standard medium was transitioned to the individual WWs, Fig. 1. Then biofilm populations shifted from filamentous cyanobacteria and green algae (Chlorophyta) towards unicellular Diatoms (Bacillariophyta) and green algae. All ATS maintained as a stable batch-culture with weekly harvest cycles from July to October, despite harsh weather events. Operational conditions, such as flow rate, WW admixture and sensor mounting, were adjusted to the specific location and WW type, but maintained a comparable setting. Due to the high content of total suspended solids, concentrations were adjusted to 1% (v/v) for unfiltered biogas-effluent, pig and cattle manure, respectively. In contrast, municipal WW was directly pumped from a secondary sedimentation basin onto the ATS and discharged into a polishing pond. In a representative batch, 47% of total nitrogen (NH4+ 0.6; NO2- 0.1; NO3- 0.6 mg L-1) were recovered from the mWW in a single flow-through, Fig. 1. In 7 days, the ATS yielded a biomass and productivity of 238 g DW and 4.2 g m-2 d-1, respectively, Fig. 1. ATS with pig-, cattle- and biogas-effluent medium yielded comparable biomasses of ~223, 240, and 286 g DW, respectively, Fig. 1. However, the ash-content varied significantly between the mWW (43.2%), pig (31.9%), cattle (46.4%) and biogas (36.7%) medium, due to the varying share of diatoms in the individual biofilms, Fig. 1. Likewise, the elemental composition and N:P:K ratio of the biomasses varied for the WWs. Biomass in PM gained the highest carbon content and N:P:K ratio of 36% and 10:5:1, respectively, Fig. 1. These biomasses were processed for long-term fertiliser experiments with ryegrass, Fig. 1. Preliminary results showed comparable crop performance and yields for mineral and ATS-biofilm fertiliser, respectively (Siebers, 2019). Detailed results to the nutrient transfer from WW to ATS biofilm to crop, as well as to potential human and environment risks will be provided.
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