Calimera Biogas Plant – High Gas Yield with OMSW Waste and Low Energy Consumption

Arciplug®’s biogas plant in Calimera, Italy, is designed to process challenging organic municipal solid waste (OMSW) with high levels of contamination. The facility utilizes advanced PLUG FLOW technology to achieve high biogas yield with low electricity consumption.

Due to limited available land at the site, a compact reactor footprint was essential. Arciplug®’s PLUG FLOW design meets this requirement while enabling high-efficiency performance in a small space. The reactor was engineered for significantly higher operating pressure compared to traditional designs, running reliably between 20 to 70 mbar. Thanks to this design, the system requires no external gas storage.

With Arciplug® PLUG FLOW technology, a wide range of complex feedstocks can be processed efficiently – even those with high impurity levels.

The system’s flexibility supports stable operation and consistent methane output, making it ideal for municipal waste streams.

The plant contributes to local climate goals by significantly reducing methane and carbon dioxide emissions. Instead of landfilling or incineration, organic waste is converted into renewable biomethane. The resulting digestate is used as solid fertilizer in agriculture, closing the nutrient loop and supporting a circular economy.

In Calimera, the digestate is co-composted together with garden waste, wood chips, and approximately 30% mature compost from previous batches. This process enhances stabilization and improves the hygienic and structural quality of the final product, resulting in a stable compost ready for agricultural application.

PLUG FLOW Technology & Key Numbers

The Calimera plant applies Arciplug®’s patented PLUG FLOW digester to treat 54.5 tons of organic municipal waste per day – amounting to a total of 19,905 tons annually. The system is engineered for high-solids digestion, using a dry fermentation process without dilution water, and is technically capable of processing over 90 tons per day, depending on feedstock (ODM) availability and operational strategy.

The single reactor is 32.2 meters long and provides 1,800 m³ of active volume. Designed for structural pressure loads far beyond typical operating conditions, the system enables in-reactor gas buffering at 20–70 mbar without an external gas holder.

While operation patterns vary based on local needs, the installed capacity delivers up to 2,464,900 Nm³ of biogas annually, equivalent to 23,910 MWh of energy. The system is optimized for low parasitic load and high methane yield even with variable and impurity-rich feedstock.

Engineering Highlights

Structurally pressure-tolerant reactor — withstands spikes up to 5–8× operating pressure for safe internal gas buffering
Integrated gas storage inside the reactor — no external gas holder needed, even on restricted plots
Stable operation at 20–70 mbar with built-in pressure regulation and energy resilience
Tolerates impurity-rich OMSW with minimal downtime and high methane yield
Compact layout – ideal for space-constrained or urban locations
External drive units and service points enable safe maintenance during operation
Fully automated control system supports unmanned weekend operation and reduces OPEX

Delivery Scope & Project Partners

The Calimera plant was delivered in collaboration between Arciplug® and its engineering subsidiary Arcineer. While Arciplug® was responsible for the PLUG FLOW reactor design, process engineering, and automation, Arcineer supported the delivery and assembly on site.

Anaergia acted as the EPC contractor for the rest of the facility, overseeing site-wide construction and integration. This collaboration enabled a streamlined delivery: the plant was contracted in August 2020, commissioned in May 2022, and completed with only five months of on-site construction.

This project showcases Arciplug®’s capability to deliver high-performance digestion systems even under demanding space and feedstock conditions. The single-reactor solution provides a compact layout, low energy consumption, and robust operation with municipal waste containing seasonal variations in dry matter — 20 % TS in summer and up to 30 % in winter.

Exterior view of Arciplug® OMSW biogas plant in Calimera, Italy, showing modular PLUG FLOW reactor with external drive units and piping. — Arciplug®’s Calimera biogas plant in Italy – modular PLUG FLOW digester with external mixing system, service-friendly layout, and prefabricated steel frame construction.

Challenging Feedstock – OMSW at Calimera

The feedstock at Calimera consists of pre-selected organic municipal solid waste (SSO), which still includes visible levels of contamination such as plastic bags, inert materials, and packaging residues.
Arciplug®’s PLUG FLOW design is engineered to tolerate these impurities with stable digestion, minimal downtime, and low parasitic energy use — even when dry matter content ranges between 18 % and 45 %, as commonly encountered in organic waste streams.

Contaminated organic municipal solid waste (OMSW) feedstock with plastic bags and leaf waste at Calimera biogas plant. — Challenging OMSW feedstock at Calimera – including plastic contamination, efficiently handled by Arciplug®’s PLUG FLOW design.

Front loader operating inside the Calimera biogas plant with mixed organic waste and processed fractions. — Inside the Calimera biogas plant – processing mixed organic waste with visible impurities using robust high-solids handling infrastructure.

Garden and pruning waste stored at the Calimera biogas plant for co-composting with digestate. — Garden waste at the Calimera site, later blended with digestate and mature compost to produce high-quality compost.

Key technologies

Delivery included: a PLUG FLOW reactor and additional equipment for Calimera biogas plant.

Digester feed: raw material is pre-selected SSO (source-separated organics).

Plant processing capacity: 19,905 tons/year and 54.5 tons/day (average) — with design capacity for up to 90 tons/day, depending on feedstock availability and operational mode.

Biogas yield: 2,464,900 Nm3/A with Energy content: of 23,910 MWh/A.

Pre-manufactured wall elements: frames, beams, pylons, mixing arrays, valves etc.