Upcycling of recycled minerals from sewage sludge through black soldier fly larvae (Hermetia illucens): Impact on growth and mineral accumulation.

Phosphorous (P) resources are finite. Sewage sludge recyclates (SSR) are not only of interest as plant fertilizer but also as potential source of minerals in animal nutrition. However, besides P and calcium (Ca), SSR contain heavy metals. Under EU legislation, the use of SSR derivatives in animal feed is not permitted, but given the need to improve nutrient recycling, it could be an environmentally sound future mineral source. Black soldier fly larvae (BSFL) convert low-grade biomass into valuable proteins and lipids, and accumulate minerals in their body. It was hypothesized that BSFL modify and increase their mineral content in response to feeding on SSR containing substrates. The objective was to evaluate the upcycling of minerals from SSR into agri-food nutrient cycles through BSFL. Growth, nutrient and mineral composition were compared in BSFL reared either on a modified Gainesville fly diet (FD) or on FD supplemented with either 4% of biochar (FD + BCH) or 3.6% of single-superphosphate (FD + SSP) recyclate (n = 6 BSFL rearing units/group). Larval mass, mineral and nutrient concentrations and yields were determined, and the bioaccumulation factor (BAF) was calculated. The FD + SSP substrate decreased specific growth rate and crude fat of BSFL (P < 0.05) compared to FD. The FD + SSP larvae had higher Ca and P contents and yields but the BAF for Ca was lowest. The FD + BCH larvae increased Ca, iron, cadmium and lead contents compared to FD. Larvae produced on FD + SSP showed lower lead and higher arsenic concentration than on FD + BCH. Frass of FD + BCH had higher heavy metal concentration than FD + SSP and FD (P < 0.05). Except for cadmium and manganese, the larval heavy metal concentration was below the legally permitted upper concentrations for feed. In conclusion, the SSR used could enrich BSFL with Ca and P but at the expense of growth. Due to the accumulation of Cd and Mn, BSFL or products thereof can only be a component of farmed animal feed whereas in BSFL frass heavy metal concentrations remained below the upper limit authorized by EU.

Sediment yield estimation and evaluating the best management practices in Nashe watershed, Blue Nile Basin, Ethiopia.

Sediment yield estimation along with identification of soil erosion mechanisms is essential for developing sophisticated management approaches, assessing, and balancing different management scenarios and prioritizing better soil and water conservation planning and management. At the watershed scale, land management practices are commonly utilized to minimize sediment loads. The goal of this research was to estimate sediment yield and prioritize the spatial dispersion of sediment-producing hotspot areas in the Nashe catchment using the Soil and Water Assessment Tool (SWAT). Moreover, to reduce catchment sediment output, this study also aims to assess the effectiveness of certain management practices. For calibration and validation of the model, monthly stream flow and sediment data were utilized. The model performance indicators show good agreement between measured and simulated stream flow and sediment yields. The study examined four best management practice (BMP) scenarios for the catchment's designated sub-watersheds: S0 (baseline scenario), S1 (filter strip), S2 (stone/soil bunds), S3 (contouring), and S4 (terracing). According to the SWAT model result, the watershed's mean yearly sediment output was 25.96 t/ha. yr. under baseline circumstances. The model also revealed areas producing the maximum sediment quantities indicating the model's effectiveness for implementing and evaluating the sensitivity of sediment yield to various management strategies. At the watershed scale, treating the watershed with various management scenarios S1, S2, S3, and S4 decreased average annual sediment yield by 34.88%, 57.98%, 39.55%, and 54.77%, respectively. The implementations of the soil/stone bund and terracing scenarios resulted in the maximum sediment yield reduction. The findings of this study will help policymakers to make better and well-informed decisions regarding suitable land use activities and best management strategies.

Assessing the Water Quality of Lake Hawassa Ethiopia-Trophic State and Suitability for Anthropogenic Uses-Applying Common Water Quality Indices.

The rapid growth of urbanization, industrialization and poor wastewater management practices have led to an intense water quality impediment in Lake Hawassa Watershed. This study has intended to engage the different water quality indices to categorize the suitability of the water quality of Lake Hawassa Watershed for anthropogenic uses and identify the trophic state of Lake Hawassa. Analysis of physicochemical water quality parameters at selected sites and periods was conducted throughout May 2020 to January 2021 to assess the present status of the Lake Watershed. In total, 19 monitoring sites and 21 physicochemical parameters were selected and analyzed in a laboratory. The Canadian council of ministries of the environment (CCME WQI) and weighted arithmetic (WA WQI) water quality indices have been used to cluster the water quality of Lake Hawassa Watershed and the Carlson trophic state index (TSI) has been employed to identify the trophic state of Lake Hawassa. The water quality is generally categorized as unsuitable for drinking, aquatic life and recreational purposes and it is excellent to unsuitable for irrigation depending on the sampling location and the applied indices. Specifically, in WA WQI, rivers were excellent for agricultural uses and Lake Hawassa was good for agricultural uses. However, the CCME WQI findings showed rivers were good for irrigation but lake Hawassa was marginal for agricultural use. Point sources were impaired for all envisioned purposes. The overall category of Lake Hawassa falls under a eutrophic state since the average TSI was 65.4 and the lake is phosphorous-deficient, having TN:TP of 31.1. The monitored point sources indicate that the city of Hawassa and its numerous industrial discharges are key polluters, requiring a fast and consequent set-up of an efficient wastewater infrastructure, accompanied by a rigorous monitoring of large point sources (e.g., industry, hospitals and hotels). In spite of the various efforts, the recovery of Lake Hawassa may take a long time as it is hydrologically closed. Therefore, to ensure safe drinking water supply, a central supply system according to World Health organization (WHO) standards also for the fringe inhabitants still using lake water is imperative. Introducing riparian buffer zones of vegetation and grasses can support the direct pollution alleviation measures and is helpful to reduce the dispersed pollution coming from the population using latrines. Additionally, integrating aeration systems like pumping atmospheric air into the bottom of the lake using solar energy panels or diffusers are effective mitigation measures that will improve the water quality of the lake. In parallel, the implementation and efficiency control of measures requires coordinated environmental monitoring with dedicated development targets.

Degradation kinetics and COD fractioning of agricultural wastewaters from biogas plants applying biofilm respirometry.

Stormwater runoff from agricultural silo facilities can be heavily polluted and needs to be treated before discharged. This study investigates biological treatability and kinetic constants of characteristic silo runoffs, applying attached growth systems. For this, respirometry measurements, typically applied in the activated sludge systems (ASM) as a suspended growth, were modified by using adapted biofilm carriers. This allows a determination of degradation kinetic of the biofilm system and a COD fractioning at the same time, which are fundamental values for the design of a full-scale plant. The developed respirometry method was compared with the state-of-the-art method using suspended growth systems and domestic wastewater. Results are comparable with the parameter of the ASM. As stormwater runoff is usually a mixture from different pollution sources, various, typically occurring substrates are investigated regarding degradation kinetics and COD fractions. Wastewater polluted with digestion residue and solid manure showed similar COD fractions as domestic wastewater with an inert fraction Si of 5-6% and a comparatively low rapidly degradable fraction SS of 21-27%. However, wastewater from corn or whole crop silage showed significant better degradation efficiencies and kinetics with an Si of 2-3% and a rapidly degradable fraction of 56-57%. As COD concentrations up to 5000 mg L-1 for stormwater runoff and up to 60,000 mg L-1 for silage effluent can be expected, the results not only show the necessity but also prove the feasibility of biological treatment of stormwater runoff from silo works and provide design parameters for adapted treatment systems.

Kinetic of denitrification and enhanced biological phosphorous removal (EBPR) of a trickling filter operated in a sequence-batch-reactor-mode (SBR-TF).

Due to their limited ability for nutrient removal, trickling filter systems (TFS) have almost fallen into oblivion today, even though they are robust and energy-efficient treatment systems. The advantage of this process technology, however, is the sessile biomass, which allows long periods of starvation without rinsing out the biomass. Therefore, this technology is promising for treating organic-polluted, intermittent stormwater-runoff. Several combinations with activated sludge systems (ASS) use the trickling filter as pre-treatment, requiring two separate treatment systems. This combines the advantages of both systems, but is paid with increased investment costs and space requirement. Due to these concerns, a trickling filter was developed that allows a nutrient removal without an additional ASS and exemplary tested for treating stormwater runoff of a silo facility. Beside aerobic conditions, anoxic and anaerobic steps have to be ensured during the process for nutrient removal. For this, the TFS is ponded with a mix of purified wastewater from the secondary clarification tank (containing nitrate) and untreated raw water (containing degradable COD). This allows both, an integration of upstream-denitrification and enhanced-biological-phosphorous-removal (EBPR). During the anoxic step, nitrate removal rates of 0.8 kgCOD m-3 d-1 can be expected, whereas a maximum COD removal rate of 4.5 kgCOD m-3 d-1 are achieved. To support complete nitrification of ammonia, a COD removal rate below 0.5 kgCOD m-3 d-1 is recommended. The anaerobic/aerobic PO4 uptake rate of the EBPR was 31%. These results show that a combination of trickling filter with ASS in one single reactor is feasible.

Anaerobic treatment of residuals from tanks transporting food and fodder.

The anaerobic digestion of wastewater from the cleaning of tank cars transporting food and fodder was investigated in both bench and pilot scales with a single-stage, mesophilic (39 °C), completely mixed process. The promising results lead to the planning and building of a 1200-m3 full-scale biogas plant at TS-Clean cleaning station in Fahrbinde, Germany. Due to softened water used in the cleaning of the car tanks, the alkalinity in the digester decreased as predicted by the physicochemical model developed for this treatment process. The model showed that 2.4 kg NaHCO3/m3 of wastewater has to be added in order to control digester pH at 7.2 and to maintain the digester alkalinity at 3.1 g CaCO3/L. In a laboratory study, the decrease of alkalinity caused a volatile organic acids accumulation and pH drop below the optimal range. In this case, if chemical buffering was not added into the digester, the digester deteriorated. In a 3-year investigation, we confirmed that the strongly polluted WW from the cleaning of tank cars transporting food and fodder is suitable for an anaerobic treatment if the organic loading rate is controlled below 4 kg COD/m3/day, digester alkalinity is adjusted by NaHCO3, and micronutrients are added despite constant considerable variations in strength and composition of the wastewater. A biogas yield of 35-45 m3 CH4/m3 of wastewater and a COD elimination of 80-90% were achieved in bench- and pilot-scale experiments and are achieved in the full-scale biogas plant. The full-scale biogas plant is working stable with a biogas yield of 68 m3 biogas/m3 of wastewater.

A combined model to assess technical and economic consequences of changing conditions and management options for wastewater utilities.

The paper presents a simplified model that quantifies economic and technical consequences of changing conditions in wastewater systems on utility level. It has been developed based on data from stakeholders and ministries, collected by a survey that determined resulting effects and adapted measures. The model comprises all substantial cost relevant assets and activities of a typical German wastewater utility. It consists of three modules: i) Sewer for describing the state development of sewer systems, ii) WWTP for process parameter consideration of waste water treatment plants (WWTP) and iii) Cost Accounting for calculation of expenses in the cost categories and resulting charges. Validity and accuracy of this model was verified by using historical data from an exemplary wastewater utility. Calculated process as well as economic parameters shows a high accuracy compared to measured parameters and given expenses. Thus, the model is proposed to support strategic, process oriented decision making on utility level.

Handling the phosphorus paradox in agriculture and natural ecosystems: Scarcity, necessity, and burden of P.

This special issue of Ambio compiles a series of contributions made at the 8th International Phosphorus Workshop (IPW8), held in September 2016 in Rostock, Germany. The introducing overview article summarizes major published scientific findings in the time period from IPW7 (2015) until recently, including presentations from IPW8. The P issue was subdivided into four themes along the logical sequence of P utilization in production, environmental, and societal systems: (1) Sufficiency and efficiency of P utilization, especially in animal husbandry and crop production; (2) P recycling: technologies and product applications; (3) P fluxes and cycling in the environment; and (4) P governance. The latter two themes had separate sessions for the first time in the International Phosphorus Workshops series; thus, this overview presents a scene-setting rather than an overview of the latest research for these themes. In summary, this paper details new findings in agricultural and environmental P research, which indicate reduced P inputs, improved management options, and provide translations into governance options for a more sustainable P use.

Experimental Assessment of the Degradation of "Unbiodegradable" Organic Solids in Activated Sludge.

In current process models activated sludge consists of biodegradable and unbiodegradable organic fractions. Recent evidence suggests that this approach may not be accurate because some of this "unbiodegradable" material may indeed be degradable. To improve sludge production predictions, it is important to know to what extent the "unbiodegradable" organic fraction is degradable. Assuming that volatile suspended solids (VSS) is a measure of the sum of biodegradable and unbiodegradable organic solids and the integral of the oxygen uptake rate (OUR) is representative of the biodegradable organics, the combination of these measurements can be used to predict the change of unbiodegradable organic solids within an aerobic digestion batch experiment. This procedure was used to estimate degradation rates of "unbiodegradable" VSS between 0.006 to 0.029 d(-1). The advantage of the proposed method is that the degradation rate can be determined directly based on measurements and relies on a limited number of assumptions.

Estimating nitrifying biomass in drinking water filters for surface water treatment.

The objective of this work is to estimate active nitrifying biomass and its main influencing factors in low-loaded biofilters based on operational data. An analytical approach based on balancing growth, decay and biomass removed by backwashing is proposed. The method is developed and applied in pilot-scale rapid sand filters for drinking water treatment. Decay rate was measured directly in the filter for different temperatures. To assess the amount of active biomass in backwash water, a technique based on respiration measurements was used. Backwash losses increased overproportional with balanced biomass in the filter. The impact of both parameters on active biomass is quantified exemplarily for a given constant nitrification rate.